An open system. I can stream content to my (or anyone's) PS3, Xbox, or any media server without ATV, or even with ATV.
USB is nice like you mentioned. If you plug a mouse into an Android device an actual mouse cursor pops up on the screen. Anything works, keyboards, game controllers (Xbox, ps3, wiimote but that's using BT), etc.
You can have adobe flash if you choose. So when browsing a forum the video actually plays in the box that was posted so you can continue to read and listen and watch the video.
Easy downloading outside the market. So you can download files you may want for another device or computer then share it later or with Dropbox or something. This also makes it easy to download and run game roms. This is N64's Goldeneye hooked to my TV I also have the basics like Mario and etc too PS 1 games.
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I really prefer the widgets on a tablet. The screen is way to big just to have icons. I can't really show you a picture because my email widgets are on there but it's nice to have live data (email, Facebook, stocks, weather, etc) in that space not just static icons.
A lot of Google apps are watered down on iOS and are really nice on Android. Esp. maps which seems to be the biggest current topic.
This stuff doesn't require root. I guess I could get a lot of that functionality by jail breaking but I don't think I should have too.