As far as the data goes, I have no idea why they went with XFire numbers when you can just log into Dota 2 and it shows you the number of unique players this month right on the front page. Which, for the record, is at the moment very slightly higher than 3,111,000. Which is a large number, considering it's not technically "out", but it's not as big as LoL.
As for the complexity, I used to play LoL quite a lot, but I never see myself going back. I got bored sick of LoL after maybe 50-60 hours of playing it, but I'm well over twice that in Dota and have no desire to slow down any time soon. To me, the complexity is what makes it so good. It's the same reason I like AI War so much, you never stop learning. There's also the discussion of how Dota already has more features in it than LoL did/does, but that's another argument (I'm talking about things like how it came out of the box with replay support, and it was a while later until LoL added that, the talk of offline LAN play, voice chat, map whiteboard, custom item builds/guides, etc).
Well even though DotA 2 is in beta, it still offers many more features than LoL has after being released for 3+ years.
Voice chat is a huge one. People can make 8 million excuses for this, or say that it's not in the spirit of "a nice community", or whatever else, but the fact of the matter is that voice chat increases the amount of teamplay and coordination in a game dramatically. It rewards people who can lead and coordinate well with their team. The human voice is vastly more effective at getting people to listen than anonymous text over the screen, which can often be ignored on accident in the middle of a heated battle or laning phase. If voice chat was really that prone to abuse, Riot could leave it off by default (like all chat is right now), but turn it on for those people who want to work better with their team.
LoL still doesn't have an official replay system yet...DotA has a replay system that saves every replay of every matchmaking game played, and then makes it available to the public for later viewing, while also keeping track of the stats and players of the match. Even if Riot releases a client-based replay system within the next year, I somehow doubt it will have anywhere near this functionality. It will probably only record your own matches, which you can then watch later, but you can't look through a database of millions of others on a whim.
In addition to that, DotA 2's spectating mode is top notch. Not only can you follow each individual player's actual in-game camera and mouse-clicks, which is cool enough (I think it's called POV camera). You can also follow any official Caster's camera movements. Or you can manually control the camera, or put it on auto-direct. It doesn't end there though, while you're watching the game, the broadcaster system is integrated into the spectator system, so you can listen to your favorite caster speak, in real time, while watching the game.
It's basically better than watching a Stream in every way. It's an INTERACTIVE stream, you still get to hear the broadcaster's voice, but you have complete control over the camera, the graphics are not diminished in any way, and you have complete control over the game's information at any given time.
Another thing DotA 2 has is item resale. If you buy an item accidentally you have 15 seconds within buying it to sell it back. In games like these, where every second counts, you're very often rushing through the shop trying to get everything you need before you're off again. One small misclick can end in disaster. It seems like I accidentally buy something on accident in every game of LoL or DotA, but in LoL I just have to resell it and take a significant loss which has actually hurt me really badly on multiple occasions. In DotA 2 I can sell it back for full price within a certain timeframe. For me at least, this is a huge feature.
From what I've played of both game's, DotA 2's bots are much superior to LoL's as well. For one thing, they have 5 difficulty settings (the final one being "unfair"), which gives players a much more diverse level of "skill" to choose from. An "unfair" bot is probably equal to a mediocre player in terms of overall competence, so if a person were to spend the time to conquer this level of difficulty before entering noob-level competitive play, they would be pretty far ahead of the curve.
In other words, DotA 2 definitely wins in the features category by a landslide. Being able to submit your own skin designs, rate the skin designs of other players, and have your designs put into the game (if they are rated highly) is amazing. Being able to create your own individualized skins in game by mixing and matching pieces from all different sets is also extremely cool. Being able to trade skin pieces (such as swords or gear) with your friends, and commonly getting pieces for free just by playing are also among some of the awesome features the game offers.
Well, when invites are literally being given away, unless you are experiencing the internet for the first time, you can find someone to get you an invite. Or if you have more money then brains, you can buy it.
That still doesn't take away from the fact that only the people seeking to play the game are going to be asking for invites. You're ignoring the power of advertising and a game which is open to everybody without having to request an invite.
Basically the only people playing DotA 2 now are the people who played DotA 1 or who were interested in the genre enough to get involved. However, when the game goes live, a lot of people who have never heard about it, or who weren't interested enough to sign up for the beta, and who have an account on Steam, will be introduced to the game.
A lot of people may be interested in it already, but just don't like playing games that are in beta. I don't blame them, I've had my impressions of many-a-game ruined by its unfinished beta state. Though to be fair, DotA 2 is in REALLY good shape for a beta, but if you had never tried it you wouldn't know that.
I'd venture to say that the majority of PC gamers know either very little or nothing about DotA 2. I've asked a lot of PC gamers on my campus who play League of Legends about it, and the just kind of look at me with a blank stare..."What's a 'Doe' 'tA'?"
I think it's a little more than foolish to think that its playerbase won't explode once it's officially released, with all the non-cosmetic content completely
free. It is the first and only ARTS/MOBA that I know of that is a completely even playing-field from minute one, and I think that will be appealing to a lot of people which are sick of the micro-transaction money-buys-power system.
I guess we'll see though.