I would guess they're banking on LTE for the iPhone 5... so in that step up you'll see a much bigger upgrade, but as a technology LTE is probably a bit immature for Apple's standards.
Sprint just capped their WiMax phone tethering and modems, they'll surely cap the phones themselves when load increases.
Sure it will: People will use it if it's there. If they don't put it in, people won't use it and will continue to laud the iPhone's battery life.