I just prefer it, I think its better, it syncs everything up very easily, the multitasking is better, its really seamless, but just the basics. Apps are terrible or nonexistent so there's not much more you can do besides what the phone brings.
I've had the iPhone 4 for six months now and so far, I really love it. It is my first smart phone, but I have played around with lots of different OS. I was actually thinking about a Palm Pre back in the days, but the phone just felt cheap and the app-situation is of course critical. OS wise, I certainly prefer iOS over Android (most people I know have Android phones now, so I do have a basis for comparison) and Symbian (though I don' know Symbian 3 which supposedly is a lot better than previous versions). I don't have too much experience with Windows Phone 7, I like the look if it, but I've heard that it's still only half way there. I also can't say much about WebOS, since I only played around with it a little in a store. So far, the only OS that felt similarly well to iOS that I've toyed around with is Samsung's Bada platform. The thing is though, that these are merely minor differences. What's most important is indeed the ecosystem. The iPhone (at least on a Mac) is incredibly easy to sync. Mail accounts, internet bookmarks, music, podcasts, address book, calendar, etc. it all just works without spending any time setting things up. One click and you're done. The only thing that's slightly more complicated is syncing the photos with the 'Aperture' software. With iPhoto, it would also work within iTunes, but for Aperture, I have to use a separate (but native) Mac app. No big deal, but it could be better The other part of the ecosystem are indeed the apps. And this is where iOS beats everybody by a landslide. So when people ask me for my subjective advice, I tell them the following: "Take a look at my iPhone and play around with it a little bit. If you think that you can't live without the apps, then go for the iPhone. A decent Android phone won't come much cheaper anyway and you won't have the ease of use or all the apps you can get on the iPhone. If you want the phone mainly for calling, texting or surfing and you don't want to spend as much money, go for the Samsung Wave with the Bada OS. It's a lot cheaper, feels very good, has a very good display and a very intuitive OS."