They started from a white piece of paper for Windows Phone 7 , so it just simple can't be done to leapfrog other platform. Because a lot of the API's build on the underlying platform. They choose to get the 90% case as perfect as possible and ship that.
Then with the power of Silverlight and XNA I'm pretty sure if the basis is stable they can easily leapfrog ahead of competition. XNA and Silverlight alow rapid development, in contract to objective C and C++ / Java the other platform are build on.
The thing is, Microsoft are telegraphing this as very much a 1.0 release (feels more like a 0.9 to me, but anyway). I'll probably do a few simple Silverlight apps, same as everyone else will - the ease of Silverlight means the marketplace will be flooded
with crap from day 1 - but I won't be recommending to anyone to buy a WP7 device.
Unless they are very cheap, there's no reason at all to buy one instead of a newish Andoid phone, or even the >1 year old iPhone 3GS. It's OK saying "what's more important, shipping or improving the APIs?", but I'm pretty sure that's not going to be the
marketing message to consumers: Hey, we just wanted to ship a phone, sorry it's all a bit half-baked, but the next version will be great, promise!