its up to the developers to make the software run on other OS's. Most don't bother because they don't think they are viable platforms. Either because of the userbase being small or the wrong demographic. Or in Apples case in the past, through a lack of hardware.
It's only in the last couple of years that apple have even had capable 3D hardware, it's starting to get some attention now, and being able to run XP on mac's and PC's is probably beneficial to both MS and Apple.
On the linux front, linux needs to interest people outside of network system admins and geeks and not have so many different versions that aren't quite compatible with one another a lot of the time.
Also outside of business, Linux attracts people who expect things for free and aren't willing to pay large ammounts for software, doesn't make much sense for a commercial developer to support it when the hours could be better put into improving the product for the 99% of people that use the software on other platforms.
It's only in the last couple of years that apple have even had capable 3D hardware, it's starting to get some attention now, and being able to run XP on mac's and PC's is probably beneficial to both MS and Apple.
On the linux front, linux needs to interest people outside of network system admins and geeks and not have so many different versions that aren't quite compatible with one another a lot of the time.
Also outside of business, Linux attracts people who expect things for free and aren't willing to pay large ammounts for software, doesn't make much sense for a commercial developer to support it when the hours could be better put into improving the product for the 99% of people that use the software on other platforms.