Its all about the money. They want to force all users into the Metro environment so they can sell you more junk software through the app store. If you boot to the desktop and have a start button, there is no use for Metro, thus one less sucker to draw into the store.
I have used Microsoft OS's since Windows 3.1, but I absolutely hate where they are going with Windows 8 and Metro. My Dell Studio Win7 laptop is now a dual-boot machine with Kubuntu 12.04. I love Win7, but Microsoft has sufficiently P*ssed me off with Metro that I've decided to divorce her ugly A$$. Kubuntu gives me what I want, when I want it and I don't have to pay her or talk to her afterwards.