In a moment of anything but wisdom Microsoft has decided to leave earlier versions of the .Net (dotnet) Framework out of the Windows 8 install, including only 4 and 4.5. The reason they give for this peculiar decision is their desire to have a smaller OS install footprint. While less disk space lost to an OS install is a very noble goal, I can think of few things worse to leave out. Any user with Windows 8 who subsequently downloads and wants to use an application written against the 3.5 or earlier .Net runtimes will be forced to install (over the 'net) a reboot-required multi-hundred megabyte installer (supporting .Net 3.5, 3.0, and 2.0). Few things deter a potential user of your software more than a lengthy download and a forced reboot.
Adding insult to injury is that I am quite sure their smaller OS footprint goal is little more than an attempt to defend against one of Apple's (and others) easy anti-Windows attacks. Unless Microsoft has radically altered the way they handle Windows Updates, their Driver Store, WinSXS, temporary files, etc. then whatever savings they claim at initial install will be gone in a few months; the Windows directory of my 1.5 year old computer is a whopping 37 GB.
Why couldn't Microsoft leave out MS Paint, MS Write, Solitaire, audio recorder, Pinball, or hell, even Internet Explorer, and include the full range of .Net support? Now us poor developers are going to need to once again need to distribute versions of our software targeting multiple runtimes just to ensure most users don't have to do the absurd .Net installs.