Microsoft is doing some pretty cool things within Windows 8 to allow you to Refresh and reset your PC to a known good starting point. This should be a much cleaner WinRE implementation than the PC Manufacture's implementations with Windows 7. It also appears to have given us USMT Hard-Link Migration for the masses.
In this related article, talking about improvements in Windows Setup, and more specifically about the new web based purchase/download/upgrade process... they mention the following:
“After this optimized package is created we compress it using an improved compression algorithm specifically for Windows 8 setup, which provides an additional 28% savings. In this example (using the Windows 7 x86 ISO) the size of the download would be reduced from 2.32GB to 1.51GB.”
Considering that the install.wim is nearly 90% of the ISO size, this seems incredible. There has to be some new .wim trickery, since modern compression algorithms run against .wim only produce low single digit percentages.