Community updates to the steam version are impossible, because the steam SDK is only released to devs under an NDA or something, so you can't expect anything new beeing released there.
Conclusion: Steam is dead, use the opensource version.
Links to (win32) builds can be found in my sig, if you don't have a compiler at hand.
Afaik you can just drop those into your aquaria(steam) install dir and it should work (but have unnecessary steam stuff disabled of course)
If you are looking for mac opensource builds, i plan to release some in a few days, but need to have them tested before.
EDIT: To answer your other question, it won't appear on steam for mac either. For mac, you can use the datafiles from the win32 version and put that together with a mac binary, and it will work too.
If you need further details about getting your hands on a bleeding edge version, just ask.