SE, Samsung, Motorola, HTC are all heavily invested in Android and are miles ahead of Nokia. They can chose to run an outside lane in that race, or they can lead up Windows Phone 7. All people with WP7 devices are just token efforts, Dell, LG aren't major players like the aforementioned companies are, HTC owe everything they have to Android. Nokia can take WP7 and become the market leader, with Microsoft investing heavily and Nokia providing world class hardware they can provide a point of differentiation as opposed to becoming one of the crowd.
I wouldn't say Samsung, Moto, and HTC are "miles ahead of Nokia". They're running essentially stock Android with crappy tack-ons that nobody cares for (when's the last time any OEM's take on Android has received praise instead of complaint?), being glacially slow with updates...
With stock Android as a starting point and, well, a clue, Nokia can easily overtake Samsung, Moto, and HTC. Just by keeping good time with Google's own updates, and developing a customized Android UI that doesn't suck, Nokia can pull ahead.
That being said, I think the WP7 choice isn't a bad one. At MS Nokia would be customer #1. At Google Nokia would be just another OEM.
