TW could do well.
Way I see it.
1) TW impose download limitation, and, in a fanciful world, also reduce the cost.
2) TW piss off the 5% of heavy users that are causing them problems. 95% of non-heavy user who stick around are happier (internet speedier now!)
heavy users move to a competitor, so now said competitor has to deal with the extra infrastructure costs.
3) Light users on competitors networks loose bandwidth to heavy users, and hear how much faster/fairer (If you like) things are at TW...
PS. I'm in Oz and really have no problem with metered downloads (but then, I'm not a particularly heavy net user - which means I'm happy to not be propping up the needs of the few).