The current incarnation of Windows Phone is actually quite good. They've taken some good ideas from existing platforms, including a few from webOS and combined them into a pleasing, attractive package. The main problem with Windows Phone is that it hasn't been able to get any traction. It is certainly not number three.
And I tend to disagree with the notion that phone UI is not important. Android for example is highly dependent on having users go to its home screen to get things done. That's one of the reasons why the inconsistencies between different carrier versions are so jarring and why the iOS UI, simplistic as it is, tends to win out over Android - particularly with non-techies. ICS goes a long way to fixing Android's UI problems. But there are so many Gingerbread, Froyo, and insert silly pastry name here handsets out there that are still in use - many of them relatively new - that will never be upgraded by their carriers. And of course even the ICS and Jelly Bean phones that do make it into people's hands have been tweaked by handset makers and carriers often for the worse.
Meanwhile iOS remains simple and consistent. Often too simple; but sometimes it's better to be simple than sophisticated. And that's why I miss webOS. More than any modern phone OS, webOS managed to be elegant - able to combine simplicity and sophistication. Even now I'm reminded of webOS's power every time I launch an app on my Android phone. There are two reasons for this: 1. Android's home screen and launcher even with ICS and Jelly Bean have always been and continue to be a mess of icons and widgets with the launcher tucked away and completely disorganized. 2. Because I discovered a very nice little launcher called Wave Launcher which mimics the webOS Wave Launcher which allows to do exactly what you say above, get the UI out of the way and just let the app take over. As with webOS, I can just swipe across the screen and launch any or widget without going back to some home screen and hunting for it. This is what kept me sane during the transition to Android and it is what keeps me on the platform today.