Tim Cook's (non)response (via TechCrunch's live blog)...

Will not comment on the roadmap." No promise of a new CDMA iPhone in summer. Tim Cook: We chose CDMA because the LTE chipsets forced some design concepts that we would not make.

When will be able to see an LTE-enabled iPhone? A. We're not commenting on unannounced product.

My guess would be batter life. The first generation of LTE chips probably suck that thing dry in a couple hours.

My guess is Tim Cook didn't want to talk about iPhone 5 features that Mr. Jobs may reveal this summer.

That would be a significant engineering change (above and beyond CDMA that they have been working on for years, and for which chipsets are mature) and would essentially make it an iPhone 4.5. LTE will certainly come to the iPhone 5, due in just a few months.