From the original MSDN blog post: "Browsers that compromise (by spreading across too many OSes and OS versions) face challenges. For example, building a new browser for the ten-year old version of Windows that came with IE6 didn’t make sense to us because of the limitations of its graphics and security architectures."
Seems like they rewrote IE's engine using newer, lower-level, hardware-accelerated APIs to achieve better performance compared to earlier versions of IE. This is at the expense of dropping compatibility support for older versions of Windows. I think they are also saying, by avoiding the use of cross-platform compatibility layers, they were able to build a faster browser compared to their competitors'.
Seems like they rewrote IE's engine using newer, lower-level, hardware-accelerated APIs to achieve better performance compared to earlier versions of IE. This is at the expense of dropping compatibility support for older versions of Windows. I think they are also saying, by avoiding the use of cross-platform compatibility layers, they were able to build a faster browser compared to their competitors'.
http://blogs.msdn.com/b/ie/archive/2011/04/12/native-html5-f...