> Back when WPF was still called Avalon, Microsoft were pushing the technology as a solution for the soon-to-be-arriving high-dpi displays

Although they were quieter about it, it has been quite clear that Apple was interested in resolution independence since at least 10.4, when such features started to show up.

Remember that very few third-party Windows applications use WPF. Most first-party stuff, even, doesn't use WPF. We're seeing on the retina Macbook that, while most Cocoa apps work well enough, most non-Cocoa apps are at least somewhat broken; imagine how much worse this effect would be on Windows, where so few apps use the current UI toolkits.