I haven't seen this question yet and just was wondering why, after paying as much as we do for service, our gigs don't roll over if we don't use them all. It wouldn't be like we were being given anything- - just full use of what we are paying for.
It's a monthly subscription that resets every month. Exede doesn't deduct overage data you consume after depleting your monthly subscribed amount from next month either. It's fair to everyone but found to be unacceptable to a few (can't please everybody).
Data and pricing structures are based on the fact that not everyone will use every byte of data that they pay for. A few will use it all and buy more. If everyone did use all of their data, I suspect data caps would be lowered for everyone. It's kinda like a college meal program. They are priced knowing that on the average, most students will skip X% of the meals for which they are entitled. Allowing roll over data would bust the marketing strategy that not everyone will use all they have paid for.