There's been renewed speculation that a new version of the iPhone is coming out this summer and possibly a Verizon version as early as September (Verizon's network uses a different protocol than AT&T's does, so making a Verizon-compatible version is no small feat).
Successive generations of cellphones are strong substitutes for one another. It's understandable why manufacturers don't announce new models very far in advance, as they immediately cannibalize sales of the current model in the interim.
But Apple seems to be in a unique situation. Its iPhone is tied to AT&T's network, which iPhone users have been complaining about for years and which has been cited as the No. 1 reason not to get an iPhone. For customers already with Verizon, it takes an awful lot to switch networks (especially if you're under Mom and Dad's plan or if you're locking into a contract), so many of them are buying other smartphones instead. I would think that an official announcement of an imminent Verizon iPhone would be enough to persuade many prospective Verizon smartphone buyers to wait a few months, and that Apple would make more money in the end from such a move.
Then again, maybe Apple isn't making promises far ahead of time for fear of not delivering. Or for fear of giving Verizon too much negotiating leverage.