J2ME does just what you suggest. They're called JSRs. I know from experience that doesn't work, because even if the platform doesn't target the lowest common

J2ME does just what you suggest. They're called JSRs. I know from experience that doesn't work, because even if the platform doesn't target the lowest common denominator, app developers will out of necessity. It's too expensive to optimize for every device. It all sounds great until there are multiple extension APIs to access the same thing, all of which are subtlety different and none of which are common across OEMs. What's even worse is when the API is shared, but each OEM implements it differently. For instance, one OEM's phones regularly return pictures rotated 90 degrees clockwise. Each problem by itself seems small, but combined they're formidable. It sucks for users too. They may hear that app X is awesome from a friend, only to find that the same app sucks on their own phone.