Want to list the real world, non-developer tasks that iPhone can't do.
In 6 months with mine, a cheapskate 3G, I haven't found one yet. Granted, I don't want to program it or program another puter remotely. I don't want to hack into Norad to find alien contact conspiracies, either. I just record complex, multitrack audio with it. Write ideas down as I get them, log my cycling using a GPS, play the odd game, read a book, listen to music, surf a bit, check mail, take photos. I keep meeting people online and IRL who tell me my iPhone can't do these things because of Apple's "walled garden". Funny, I can do them and at a fraction of the cost of some platforms. (Compare Luci Edit SD on Windows Mobile at AU$700 with iSaidWhat?! for iPhone at AU$1.19, or Multitrack at AU$20 for example.)
And one API, one development architecture, verification by Apple that the code isn't an exploit, all make iPhone very secure. PDF exploit aside (it'll be closed within the month with a simple update) most of the anti-iPhone talk on Slashdot is along the lines of, "I'd never use one because they can't do ..."
Anybody who hasn't used one for real world ongoing, everyday tasks, anybody who has only used a demo in an Apple store, isn't qualified to comment.