Apple released the first iPhone in late 2007 with only an EDGE radio while everyone else was rolling out 3G smartphones in America. They then caught on and released a 3G iPhone, followed by the 3GS and iPhone 4 that all three had the same 3G data support. The iPhone 4 doesn't have the latest HSPA+ support that AT&T is rolling out so when HSPA+ devices hit later this year and early next year the iPhone 4 will be one of the slowest smartphones on AT&T. Apple has not demonstrated that it is willing to lead in the wireless data technology so I don't think they are going to start now with LTE. LTE will still be in an early rollout phase and Verizon stated it will take up to three years to cover the US.
Apple will wait and let other manufacturers work with LTE to get the kinks out and then come in when the technology is tried and tested and throw on a good user experience. Do you honestly think Apple will roll out a LTE-capable iPhone in early 2011?