I'd never use 250GB in one month, but as others have pointed out this is just the first step in getting the cap lower and lower. Personally, I think the cable companies that provide internet are worried about how much internet TV is going to hurt their business.
What if an internet household watches Cable TV on average 8 hours a day 30 days a month (this includes kids, parents, and other household guests across multiple TV's playing at the same time) decides that they can watch all their favorite shows online via legal (or illegal) services such as Hulu, Fox on demand, and numerous other sites popping up that are ad supported and then decide to drop cable? This could cripple the cable industry's model for pay television.
A scenario like this isn't likely to happen in the next couple years but that's the stuff being talked about in board rooms and marketing. It's better to set the bar for bandwidth caps now and slowly lower them so that the scenario above never has chance to happen in the first place and if it does they can charge more for higher bandwidths and recoup the loss to the cable TV devision.
