Microsoft has had many chances to introduce clean new APIs: for instance, .NET could have been built on top of a simpler platform, or Metro could have been an opportunity to take out some cruft.
In the end Metro breaks everything (if you think the median programmer could write non-trivial apps with asynchronous I/O, think again.) Amazingly, Metro almost feels like a tablet operating system when it is running on top of the line hardware, but the ultimate attack on latency is to remove things from the stack and not to add them.
Personally I think Windows today (even Win 8) beats the pants off Linux and MacOS as a GUI operating system, but I seriously have to ask questions such as "will Intel be making new x86-compatible processors 10 years from now?" when I see Microsoft and Intel consistently painting themselves in a corner.