I have no idea if this could be one of the reasons this is happening, but about a month ago or so I read about where Comcast and some of the other big name broadband providers were going to start capping downloads to a certain amount of data a month. Their argument was that it is getting very expensive in the amount of bandwidth being used on today's internet with the very large video files.

Whether or not this has actually started is one thing..but even if it hasn't, it's something to be very concerned about possibly comming down the road.