At some point in a long living project, you have to declare some bugs are #wontfix. You are just lieing to yourself if you think you will ever get to the end of the bug backlog. It also can become an anchor, the team is focused solely on fixing bugs here and there instead of moving the ball forward (and hopefully fixing more fundamental problems along the way). I've made the call to mass close tickets like this. It's…
Then mark them as WontFix with a comment explaining why. Marking Obsolete without comment and restricting further comments is a huge slap in the face to your biggest supporters (those who went through the trouble of trying to contribute positively by filing/commenting/starring the bug).
It's a "we're sorry, for whatever reason this issue is not getting traction. We are closing it because whatever the issue or reason is, whether it's on our side or the reporter's side, or something else, this problem is not effectively handled by this issue".
Closing as WontFix would inspire a thousand proclamations of "Google is never going to fix X!" when they may very well address it in the future.
I don't think what Google's done is ideal, I agree they should add a comment. However "Obsolete" is probably better than WontFix unless they really did analyse the problem and explicitly decide not to fix it.