Yes, this is true -- but on the other hand, not being on Steam hasn't hurt some very high profile indie games. Minecraft being the obvious example, but there are a handful of others that sell as well as AI War does on Steam, but without the help of Steam. If we hit some solid numbers based on excitement from the folks who aren't "Steam or nothing," then that's enough.
One thing about Minecraft and some of the others, though, I should think: is that apparently there's no chance of Minecraft coming out on Steam, at least in the opinion of most folks, so that makes the "Steam or nothing" actually "Minecraft or not, regardless of Steam." So that might somewhat negate my point above.
Assuming that AVWW comes out on Steam, which I see no reason why it wouldn't at this point, there's no way it wouldn't have registerable keys there. We've got 5 products on Steam at this point, all with registerable keys, so I think it's pretty clear that's something that would continue. I can't promise anything on Valve's behalf or anything, but I don't know why that would suddenly change, anyway.
So, yeah. Who knows! Only time will tell.