So many "I told you so" people in this thread don't seem to realize that Retina graphics for iPhone 4 didn't appear until very late in the game, and that Apple may be purposely inserting these current-resolution images to throw everyone off (reminder: this is a beta 1 build). Do you really think they don't know what goes on after an update? All the plists that have been torn apart in a desperate bid to find a shred of confirmation there is something better coming? All the package extracting that goes on to find resource images that offer a supposed confirmation of future software funcitonality?
I'm not saying the iPad 2 will see a resolution change, but rather that many of you are jumping the gun thanks to a couple of images that may or may not reflect what's in the final product. Just because the iPhone didn't see a significant screen rez bump until a few revs in doesn't mean the iPad will be the same. Two different products, two different visions, two different competitive landscapes (this is true moreso for the tablet craze right now too).
I'm still holding out hope we'll see a higher-res screen, but if we don't, it won't be all that surprising. As it's been said, developers would probably freak out (if only initially), and Apple likes to take it slow.