imho WordPress.com has to stay the reference rather than WP.com. After all, it is a question of branding, and everybody knows WordPress now, and having it in the URL of many blogs is also part of the branding. Remove it and you destroy a part of the branding built arounf WordPress, don't you think? Unless Matt wants to rebuild completely the image of WordPress of course.

I would vote for the Mobile version of WordPress.com. There are already dozens of shortening services, Automattic just bought a good one so why bother?

But like you, I am curious about the choices from WP team! You can be sure they had an idea before to buy the domain!!