it's very easy to set up a virtual machine for testing, if that helps. no need to have an entire machine dedicated to linux. you may also find that technically-inclined players will be willing to help you troubleshoot problems.
I can understand your point and of course you're not obligated to support any particular platform though. I agree with the other poster that supplying an explicitly unsupported linux build would probably be good enough. I will probably roll the dice and buy the game, since another player said the windows version worked via wine.