[psychometry]

Windows and OS X use different methods of hinting where Windows attempts to stay true to the typeface and OS X attempts to provide a provide a smoother, more readable version. Webkit browsers give you some level of control with subpixel rendering CSS attributes, but fonts might still look awful in Firefox or IE on Windows.

[subsection1h]

It's my understanding that it is Apple that attempts to preserve the design of the typeface, not Microsoft:

http://www.joelonsoftware.com/items/2007/06/12.html

[ss64]

Also Windows 8 uses subpixel positioned grayscale, rather than subpixel positioned ClearType. When you rotate a tablet by 90degrees ClearType doesn't work.