Well, maybe not.
Marathon is a sweats game. Hardcore PvP people who play many hours per day. Just look at the Marathon OT, most of the people in there loving the game already have 50+ hours played on it. Its not a game for normal gamers, its for the hardcore. So, in that regards, hardcore gamers will schedule time on the weekends to do this. They'll order their life around it if needed.
I don't think Marathon is a game for most of us. So in that regard yeah, they'll kill any chance of the game having a broad appeal or a large audience, but the hardcore sweats will likely eat it up? Maybe.