It does make sense if they sell in a store for with support to multiple platforms and they only support the paid one.
A reminder that on last steam report, Linux overcome Mac as second in usage operating system. They don't have to excuse of only support the top 2 OS. Instead to refund is to negative review, games companies are much more affected by losing a positive rating that a refund.
Why? He is happy with his operational system. He do not need to pay 100 bucks for a questionable OS . Linux had overcome MacOs as number of users on steam. It is his right to complain. Go sell in windows store if you want be windows exclusive.
I am very happy using duply, that uses duplicity. Works well both for mounted disks or S3. I would ignore any recommendations of a sync tool like Dropbox. They will very happy propagate your problem in all your places before you realized it.
I don't know if windows is running out of our planet. But I know some Linux are in some satellite thing. So Windows is an earther problem
I do automatic testing, debug is a waste of time