I don't think they will either.My contract ends in April from my current carrier.
LTE does not factor in, mainly because none of the main companies have nationwide coverage for LTE yet. Verizon is not expected to finish their LTE deployment until 2013. Plenty of time for me to enjoy a non LTE iPhone 4. I honestly think the iPhone 5 will be a minor refresh to the line. I dont think Apple is going to bring a LTE phone when only a small minority can enjoy it. Maybe next year we will see a large upgrade in iPhone hardware.
When 3G was out and established, Apple still used Edge on its first iPhone. Then they finally went to 3G with the next revision. They won't jump on LTE especially when it's not even available everywhere.
Honestly, I don't even see the next iPhone being much of an upgrade either. The iPhone 4 is pretty good and has everything I could want in a phone. I don't know what else they can do besides add a better processor and more ram to compete with some Android phones that are coming out that are basically mini computers.