I expect to see a 1080p Apple TV this year, since the A5 and upcoming A6 can both do 1080p video. The current Apple TV is A4 based, which is limited to 720p. With the new iPad having a resolution above 1080p, Apple finally has a reason to have 1080p iTunes content.

Beyond that, Apple may not have wanted to take A5 chips away from the iPhone and iPad to sell in Apple TVs. Now that all of the new iPads and iPhones will be A6 based this year, Apple will have more supply of A5s for other devices.

None of this helps people who already own an Apple TV, however

The iTunes Store only supports 720p right now anyway, so in the Apple ecosystem it doesn't make sense to worry about 1080p. I imagine this will change soon though. (A5 based AppleTV + iTunes Store upgrades)

This may be a bandwidth issue. I remember my friend having major issues streaming 1080 to his tv box over wifi. He had to get an N router just to support it. This may be a compromise.

word on the street is that will change before summer.