i dare to say we are pretty good at low level stuff no mather what to OS is.
(We have a pretty large background in programming lowlevel stuff on various machines from 6502 via 68xxx to 80x86 and several obscure procs inbetween)

But it's not only a technical issue, it's also a commercial descision.
at this moment we indeed rather invest more time in the current project then in a new platform which in our opinion has a too small userbase to make it intressting..

HOLD ON!! i'am not saying that the other OS'es aren't good enough, i use linux everyday on my workstation and servers. But commercially it's not that appealing to us. So yes it's a commercial descision not to support other os'es then OS-x and Win32.