press release writing = work for hire?

It is work for hire, you get no copyright (who cares--it's corporate writing), and the difference between writing for a non-profit v. a corporation is the $. I don't know anything about your writing skillset, but this could be a great opportunity to add to your portfolio. Corporate and PR writers can get a few hundred dollars (or more) per press release. Try doing a google search for writing press releases.

I think when you work for hire, usually the company retains copyright.

Remember, the entire point of a press release is to have as many people use it, re-use it, and tweak it as possible to bring in more coverage for the client. So yes - you'll need to give the copyright to the client - otherwise they can't legally distribute it as intended (which is what they're paying you for).

exactly. it's business writing and press is a different ballgame.