I think it's just a question of "Will this be a thing, or will this be dropped as a dud?" Microsoft has a history of pushing hard on things (Silverlight comes to mind) and then dropping it a year or two later when it doesn't gain enough traction, so naturally Windows developers are a lot more wary of the "brand new thing".

Additionally, for better or worse, Apple's hardware cycle tends to be a lot shorter than Microsoft's-- the fact that you can't upgrade a system piecemeal pushes people onto the latest and greatest, which means it already comes supporting the software for the same, as opposed to the people still using Windows 98.