My guess is "Work" is a ploy to get Facebook un-blocked by corporate firewalls.
The business functionality has already existed (since FB uses its own platform internally), so its comparatively minor in engineering effort.
Ha! Nice theory!
No seriously, that's pretty brilliant.
Except that it's on a different domain and won't affect the facebook block.
In fact, this would actually force people to block FB. The worst thing to happen would be for someone to post important information related to company on their personal feed by mistake. If they can login to both the accounts, this is very much possible. Unless, of course, FB for work looks dramatically different from original FB. I don't know, I never tried.
I work for a Large Corp., and FB is not blocked. What is blocked are services like dropbox or google drive. But I can't imagine the security department would allow publishing work-related information to other company cloud.
Facebook At Work is not a free service.
Maybe they killed Parse because it wasn't all about keeping people in their walled garden, and enabled people to duplicate features of facebook. It could be in line with what they did with FBML & facebook apps.