Let's be clear here: there is no such thing as "just" Web programming, at least if you're doing sophisticated stuff. Each browser is different in its quirks and characteristics -- the same code, executed on IE, Firefox and Safari, will generally perform a little bit differently on each. And the iPhone is more different than most: there are a lot of assumptions about UI built into Web programming that don't hold true for the iPhone. (For instance, the notion that "hover" means something, or the keycodes returned when the user presses "Enter".)
If you're building UIs for the Web, and you want them to be fancy, responsive and cross-browser, be prepared for real work on *each* target browser. While things still aren't as bad as the early days of the Browser Wars, it's still quite a black art.
(This rant brought to you by one too many facile comments online, poo-pooh'ing the notion that Apple needs to provide iPhone developers any technical support, since it's "just Web programming"...)