In an interesting piece on his blog Craig Hunter points out:
Business aspects aside, the main issue I see as a traditional developer is that iPhone web app development is still very limited. Outside of some viewport settings, a couple special link types (really only the “tel:” link is new), and some new “-webkit” style attributes, there is little about making iPhone-specific web apps that differs from generic web apps. And that’s possibly the most disappointing aspect of all from my standpoint. Apple’s announcement states that “developers can create Web 2.0 applications which look and behave just like the applications built into iPhone”, but that’s not the case.
The retro-Nintendo game DUCK HUNT that was specifically designed for the iPhone (located here) .... looks a lot like an iPhone only app. It's not really playable on a desktop or laptop computer. I would bet that 9 out of 10 people you showed it to would say, "How did you get that on your iPhone?" .... meaning they thought it WAS an application developed JUST FOR the iPhone.
* Credit to Daring Fireball for the link