This would be all fine and dandy but there are a couple of problems here:
1> There really aren't enough of those going around to justify a central server to host the update files for OTA updating.
2> If someone volunteers to host the update files they open themselves up to possibility liability.
Think of it, when a file has to be downloaded manually the person hosting the file can put whatever disclaimers on it.. you know.. "download at your own risk, don't hold me responsible if this bricks your device, etc". With an OTA update method then it can be updated automatically and if problems happen then whoever's EE/PE just got bricked will go to the person hosting the files and say "WTF did you do to my PE!?"
Who is responsible when someone's EE accidentally OTA updates itself using a PE file?
While in theory it's all fine in dandy, in real life it just doesn't make a whole lot of sense. It's not like updates for these things are rolling out on a weekly basis or anything.