I always try to support even the most antique systems as much as possible, but sometimes I just can't anymore.
Up until now the game worked on 10.6+ but I'm soon going to use code that requires more recent compilers.
Thus bumping the requirement to 10.9 (which is already nearly 4 years old).
The steam page has listed 10.9 has a requirement for a long time now anyway so this is more an official announce than a surprise :)
Have fun in Eyal!
PS: If some mac pros can explain to me how to compile C++11 (or ideally more!) on and for OSX 10.6, I will not have to drop it ;)