PC vs MAC

[hundredpercently]

I bought my Batman AA and have played it on my PC before. However, it says its actually available for Mac as well , how do I get my Batman AA to download and work on my Mac through steam? I can't seem to be able to since it says "its not available on your platform". Is it possible that I need to buy it once again for Mac?

[Pallando]

There's no one here anymore. Everyone received the GOTY edition for free.

Your question may have more visibility over here:
http://steamcommunity.com/app/35140/discussions/

Also, Arkham Asylum is not "Steamplay": the mac version is not provided by Steam for now, but I think it might be included later.