Well if I have the option to:
a) Start the game and play
or
b) Start the game, try join a server, cannot join server need update of mod, find mod page, download mod, install mod, start game.
"We did this back in the days lets keep doing it!" - Just because we did it one way before doesn't mean its a good way :)
Btw, in the sub agreement it states:
Doesn't this mean they can only use it for showing of a game with promos and stuff in steam? Its not like they are going to sell your mod and earn money on it, I have never heard of this happening.
Edit: I honestly don't think Valve is going to hijack a mod to earn a few hundred dollars, even a few thousands extra. It's no money for them, they are probably more intressted in keeping their image good.