Apparently (i may be talking out of my anal orifice) you can use dpkg from a console.
If nokia does decide to become apple and deny any non-repo installing, i'm sure someone will create a humongous rep-of-everything, where anyone can put anything. And by "i'm sure" i mean i would personally give as big a hand as i have, just to piss off the crooks that made the decision.
But then again, the question was about iphone apps. AFAIK, most apps require system-specific utilities, like bash. For apple, it would be as easy as adding "apple-verification-annoyance" on the dependency list and kill the whole idea. Even bypassing fake requirements, you might still end up with genuine libraries the iApp needs, but maemo can't provide.
Might be worth a shot 'though