I think apple is waiting for the price of the lte chips to drop so they don't have to increase the price of their phone since they like to keep them at $199/$299.
4G LTE Devices Could See Significant Price Drop in Late 2012 - Droid Life: A Droid Community Blog I think since the 2nd gen chips will be more readily available and hopefully help with some battery issues that is what apple is waiting for. Any thoughts?
Apple is probably waiting more for the right time.
LTE networks are still being built. The cities that do offer LTE, the carriers, are still trying to optimize their networks. For a device manufacturer, the challenge is building devices that are also optimized to run on LTE. Look at todays devices and how they struggle when put into 4G mode. Apple would not dare risk taking that kind of hit to there image, just to say they have a LTE capable device.
Something people do not talk about, is developer support for the next generation networks. That has to be in place as well, to create a demand for moving into the 4G arena. That's still underway.
I believe, Apple understands the market better than most. More importantly, they have an ecosystem of products that is unrivaled. For NON Apple manufacturers they HAVE to offer devices early and often to better compete. Apple will release a next generation device at the perfect time, and you can bet it will operate to the expectations of there followers.