I got two cars for free. I'd be pretty pissed off if a stranger thought they should have them.
If we're talking moral imperatives, how many do you think are required of WP.com and how many required of the owners of those blog names? Besides, anyone so short of imagination as to come up with only ONE name that's good probably won't write a kickass blog anyway. If nothing else you can always register Whatever.Wordpress.Com and get the domain upgrade to make it SuperDuperBlogname.com.
If you want something that somebody else has, you can ask them nicely to give it to you, and if that is unsuccessful you can even ask them if they want money for it. But you can't muscle them, claiming some sort of moral high ground.