Bandwidth costs money GS. An ISP lives or dies by managing the average bandwidth per customer. If the average gets too high, the ISP makes less, or loses money.
ISP bandwidth is very expensive. Figure about $3,000 a month for 3Mb/s of bandwidth on average. If the same number of clients all of a sudden use up 6Mb/s of bandwidth, the ISP pays more and so on.
Commercial accounts (like HTC's) work the same way. The more bandwidth you use, the more you pay.