I have mixed feeling about this.
First lets start by saying that i am a TBS entusiast that in the last 5 years or so have become enjoying RTS more and more.
Now considering my background (around 15 years in gaming, around 5 of so in competitive gaming) i strongly disagree with this:
And RTS gamers are by definition people who do NOT want to play against other people
What??? By definition standard "rts" games are competitive games that shine in multiplayer *ONLY*.
Pick Starcraft, Warcraft, Total Annihilation, Supreme Commander, Company of Heroes, Dawn of War, Dawn of War 2 or whatever other popular RTS and you'll see there are the singleplayer guys and the competitive guys.
The singleplayers can claim to be expert, to have passed hundreds of hour playing but are -no matter what- complete newbie to the game till they can compete and win vs other players.
That is simply because there is not yet a noncheating ai capable of challeinging/beating a veteran player in any of those games.
Singpleplayer people can have beaten all the campaigns and won all the skirmishes but when they go online they are kicked in the ass. Period.
Now every people have fun in different ways and its perfectly fine to enjoy a game in singleplayer only either for lack of time, lack of skill, lack of patience, poor design, whatever but imho rts till arent played online arent really enjoyed at their fullest.
Now after this disgression i fully agree that growing up the major problem is the time needed to dedicate to a real multiplayer experience.
For instance i was once in the top10 ladder of Supreme Commander by playing dozens of game every day. Now i have time to play a couple a month and i'm nowhere near the skill level required to be in the top100 anymore.. it was basically a work to remain competitive and i cant afford it anymore so i just play for "fun" still knowing i'm not mastering the game anymore.
Ai War offer a very different experience than most game, there is no equal start of the players and the other ai players [something that i really miss] but still is enjoyable.
Still for how the game is designed if there were a competitive option which imho could be added with just some minor work to the existing core mechanics it would lure a quite larger playerbase just by having the option there (even if not played by many people).
At this moment the lenght of the game is the main minus to have multiplayer. When and there is a fast option with some mechanic change to have a game over in 1 hour or less than we can talk about multiplayer, till then singleplayer is the only real choice.