Exactly. It really does go with any genre, that sort of statement. Usually when someone says something like that, I just say the same thing, but insert *their* favorite genre into the phrase, and then repeat until they stop saying it. But that's me and I can be annoying.
Didn't really want to get into this discussion but now I feel compelled.
If you take 5 different games from the Platformer genre:
1.Metroid
2. Megaman
3. Mario
4. Spelunky
5. Limbo
Sure, there's some small differences in feel and weaponry, but ultimately you control one character that moves across platforms and shoots things. You can add some neat roguelike things like to Spelunky does to make it more interesting, but it still boils down to the same game with some extra replay value.
Let's look at 5 games from the RTS Genre:
1. AI War
2. Total War Series
3. Planetary Annihilation
4. Faster Than Light
5. Command and Conquer
Holy shit, these games could not be more different. If you think AI War is ANYTHING like Faster than Light, or that Faster than Light is ANYTHING like Planetary Annihilation. Well, let's just say you should devote your brain to science because you're living in an alternate universe.
These games are so fundamentally different from each other, you could play one for thousands of hours and still be shit at all the rest of them. The same is obviously not true of Platformers. Any skill you generate in a Platformer will translate at least partly to another game because let's face it, it's all the same game with minor differences.
Anyway, not to derail the thread, but I'm calling you out on being delusional if you want to say that EVERY genre is just as repetitive and uninspired as all the rest. You can repeat that as much as you want to, but it doesn't make it true.
Some genres are known for being repetitive and uninspired (Fighting games, puzzle games, MMOs), and some like RTS and roguelikes have a lot of successful experimentation in terms of what has been accomplished with them.
I wouldnt be so sure.
Alot of it is very subjective. I'm going to take a wild guess and say that you dont play much in the way of platformers, because I see that aspect in the same way you seem to see RTS games. Mario and Metroid, playing ALIKE? What? N... no. Not even close. Having played both of them extensively, over and over again.... yeah. Not even close.
But I look at most of the RTS genre, and.... I see the same game, repeated over and over. Starcraft, Command and Conquer, Total Whatever, and that Planetary thing, or whatever.... to me, all the same. I just see the same things, repeated over and over... click, click, click, click. Set up squads, then do gameplay made of hotkeys and wild clicking and more hotkeys, crash a bunch of explody things into other explody things... yada yada yada. The only one I bother with is AI War, because A: it's an Arcen game, and B: it's known for having a single-player mode that isnt terrible. But even then, I see huge similarities with that and what I know of the rest of the genre.
Hell, just to illustrate, I'll adapt a sentence you used: "Sure, there's some small differences in feel and weaponry, but ultimately you control an army that can be divided into smaller groups, and clashes with another army, often with a 'rock-paper-scissors' sort of thing going on between units". As one that mostly ignores the genre and really doesnt give a damn, this is how I see it. No exaggerations here.
But that's the thing: I dont know enough of it, or PLAY enough of it, to be able to accurately comment on them.
It's the same with fighting games for me like it is with platformers. Street Fighter VS Guilty Gear or Blazblue, for instance. Nothing alike at all. They're both in 2D, and characters have various moves.... and that's about where it ends. Dont even ask me to explain this one. That'd be an incredibly long rant, even for me.
Same with shmups. To many, something like Touhou will look alot like Cave's games, which may look like Psikyo's games, which may look like others.... even when none of these play anything alike. Hell, even among the same developer; something like Dodonpachi DaiOuJou plays NOTHING like Dodonpachi Daifukkatsu (as such, I haaaaate DaiOuJou, but looooove Daifukkatsu) and those are both from the same SERIES. And you KNOW I've played those enough to be able to accurately make such comments.
I'm not delusional. But I'm also very aware of the subjective nature of things like this. To some degree, one must be "into" a genre (and like it enough) to really grasp everything about it. Hell, FPS games are another great example: They're SO similar to me that I'm incapable of telling them apart. That's not an exaggeration either. Halo, CoD? Same damn game. First person, has guns, bang bang bang, take cover, BOOM HEADSHOT ZOMG, blah blah blah. Not interested, so I cant be bothered to learn more. But I'm also aware that this is WHY I see them that way. If I were interested enough to jump in, I'd learn how and why they're different. But I am not, so I wont, so.... there ya go. I usually just call all of them by the sarcastically generic name of "Call of Halos", because I can be unpleasant that way.
And hell, you can go REALLY far and look at it from the point of someone that isnt a gamer whatsoever. I've found that alot of games.... from ENTIRELY DIFFERENT GENRES.... look basically the same to some people that really just arent into / dont care about / dont understand gaming. The games dont have to even LOOK remotely similar. They're still 'the same things". Hell, I tend to look at movies and TV this way. It's all the same to me, just the same crap, over and over (needless to say, I dont like movies or TV one bit). But again, I'm well aware of why I think that way.
So yeah. The idea of "if you've played one of (insert genre here), you've played them all" really CAN be attributed to absolutely any genre. It's subjective... it depends entirely on the individual... not the genre.