[experimental]

"Windows goes even further: you can click through a link or button on a non-focused window."

This is a interaction design mistake. On Windows, if you click inside an unfocused window you can perform an action otherwise unintended, Mac OS X's way and Haiku's (www.haiku-os.org) is correct. Interestingly Firefox follows the Mac way, but on at least Windows Chrome does not, and if you happen to unintentionally select the close tab button, you're tab close and if you're in Incognito mode, you lose that tab because there is no history.

[iaskwhy]

I understand your point of view but just because you might do something by accident it doesn't mean it's a design mistake. There's some advantage for each method, I prefer to make a mistake a day a week than being forced to click twice everytime I'm using side-by-side windows (like when I'm writing code and testing).