Really? a 4GB plan over a month is roughly 133 MB a day. Lots of people use more than 4GB in a month, which equals more than 250 MB in two days. Why do you think so many people want unlimited data? Is it because they plan on using less than 4GB in month? If the "average" consumer uses 1GB in a month they'd go over that 250MB data plan multiple times.
Sorry for not using power users as benchmarks. I am truly sorry. I forgot that "most" nowadays equate "a few", and substantially less than "average and below". By your figures alone, we can easily conclude that i was right. Most people do not blow through 250MB in 1-2 days.
And if people want to use more - they can buy more. Whats the problem?
Plus, knowing Amazon - i am sure that you'll get free downloads from their site anyway. If you ever feel the need to stream video on the fly, that is (gainsharing that revenue would be more profitable for all parties involved).