I see a bunch of people saying "I'll only pledge $1, until they say they'll have Linux support", which kinda misses that if they don't reach their goal, there's *no* chance for Linux support.
Does it come down to asking Linux people to support the Windows version, on a maybe? Yeah, it does, and no it isn't really 'fair'. They could always say "no" outright. Stating the maybe, and the limitations, because *people asked for that information* seems better than a no, to me.
It boils down to a question of 'Do you think it is a game that should be made, even if it might not happen on your favorite platform?'. If yes, then pledge, if not, don't.