I know it's not listed on the game card but any chance this might unofficially work on Windows XP?

Aww, that's too bad. Thanks for the info though.

I see this developer mentality "let's take a really old game and make it work only on windows vista" has arrived also on GOG. Sad :-(.

I missed a lot of the classic brawlers on other stores because of this. Not going to buy this either.

So, it's most likely programmed using DirectX 10 or 11.

I ran into this with 1001 Spikes which is OpenGL 3.x. If you're on an OS (such as XP) which is not receiving video driver updates anymore, and thus does not have a certain OpenGL version available, or, in the case of DirectX where the version available is tied to the OS, then you get cut off purely from the developer having chosen a newer graphics API to work with as the base for programming. The sad thing is, as a game engine developer myself, I know for a fact that OpenGL 1 (yes, 1!) or DirectX 5 would technically achieve the same effect if we're just talking 2D graphics engines.

Networking may be a different story however, which may be the cause of the choice. That or the mentality "who's using an old OS anymore?" The former I can live with. The latter I find reprehensible. Agreed. Well, there's always MAME for you. Pure emulation, no remake, and no compatibility issues with XP.