It's a horrible article and misleading title. Sending different CSS based on the browser UA doesn't equal not supporting a browser. In fact, just the fact they are doing that shows that they are still supporting IE7 by not pushing features that would be broken to it.

That being said, I would guess that bug fixing and the like for IE7 are probably prioritized lower, hence things like the busted layout shown in the article picture.

I'll wait for the official announcement from Facebook, just like they announced when they would stop supporting IE6.