Given this is a Ren'Py title, there's simply no reason not to offer Mac and Linux packages. It'll just work on those platforms. While I don't particularly mind dropping the game into Ren'Py to create a native Mac app, you're losing out on an audience who doesn't even know that this is possible and won't buy the game at all because of it.
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Nice. And thanks for reading through my brain-addled typo. Yes, it was Mac that was missing. As for testing Linux, you can get free virtualization s/w such as VirtualBox and then one of the more popular Linux distros, also free. That said, the Linux guys are also more likely to build their own native app with Ren'Py.
Cheers on a successful 2nd chapter.