need to buy the game for each platform???

[hero1900]

i just has this problem when steam has the discount on the game i was checking desura for a discount since i am using linux and actually i didnt check the game website it self soi waited for 2 weeks to see if it will be discounted on desura but nah . so i decide to get it from steam and i play it through wine with no big issues. but of course i want a Linux version. now you can answer my subject do i have to buy the game separately for each platform ??