And the advantage of going with WP7 is that it keeps Apple and random patent trolls from coming after you since Microsoft indemnifies OEMs against software patents. Not to mention the estimated fees are only about $12 to $15 which weakens GPs argument that cost is a big factor.

The OEMs and carriers do lose the freedom to develop a UI skin (which delays updates) and load always-running and uninstallable junkware though which might count for something against WP7.