Everybody who went to Google I/O has probably played around with the Nexus 7 tablet for at least a week now. They may have noticed that the display is pretty great, and that apps built for phones actually look pretty great on the larger 7-inch screen. There's a reason for that which Googler Dianne Hackborn explains in a lengthy Google+ post.
First and foremost, Hackborn begins the discussion by saying that the Nexus 7 has "an interesting screen." Interesting can be a good or bad thing, Hackborn, which is it? In her explanation, it's definitely a good thing as she says that it has a resolution of 1280x800 with tvdpi density. Why would a pixel density built for TVs be used for a tablet? It's quite simple really.
The tvdpi technology was built for Google TVs at a resolution of 1280x720. People build Android apps that can be viewed on a TV at that resolution without any blurriness. By using tvdpi in a 1280x800 tablet, developers can create apps that look better on the screen than the usual mdpi density that you see on other 7-inch tablets.
Hackborn says that tvdpi especially helps with the Jelly Bean UI. The UI on the Nexus 7 is somewhat of a Frankenstein as it takes parts from both the 10-inch tablet UI and the phone UI. It really depends on what works best for the resolution you'll see on the Nexus 7. The navigation bar, for instance, is lifted from the phone UI, while Gmail uses the tablet UI in the conversation list.
So what does this all mean for developers? You won't have to support another pixel density with your apps. Android has powerful scaling software in place that will automatically make your app and all its related content (including bitmaps) look great on the 1280x800 display. Font sizes will also be scaled to fit whatever resolution the content is being displayed on.
Here's a simple breakdown of what the Nexus 7 offers to developers in terms of scaling:
Hackborn concludes by saying that the Nexus 7 was their big experiment to see how well Jelly Bean could handle scaling. She seems pleased by the results and all the reviews coming out of Google I/O seem to indicate that the results are satisfactory to the regular user as well. It looks like Apple's argument of apps built for iPad look better than apps on Android tablets might soon be a thing of the past thanks to better scaling that can accomodate all screen densities.