I think that the reason the Affinity is Mac only is more skin deep than anything. It seems to use a lot from the CoreImage and Cocoa frameworks built into OSX. That is why it feels so snappy, it isn't loading multiple libraries to draw the shapes, rather than just using what is built into the OS. Although it may be disappointing that there is not a Windows version, the fact that they can concentrate on taking full advantage of built in libraries instead of patching it up to work on both, or just plain leaving something out is a good thing.
