Beyond what my blog post states, that Melanie referenced, even if Microsoft attempts to take out the competition, there's a lot of legal issues that are going to (and already have) arisen. As linked in my post:
People are already threatening to sue Microsoft for anti-trust violations if Secure Boot eliminates the Linux possibility. But, the only people this is even going to effect in the beginning is the consumers. Most businesses run old hardware as it is, and if Windows 8 requires Secure Boot, then businesses are going to have to wait for their next IT deployment/restaging.
I personally don't think people are looking at the big picture here, but is basically just eyeing what is being said (remind you, its all vague). Will this change the way IT is? I don't see any other way around it. Is Microsoft going to purposely put themselves into legal issue? I don't see how that'd make a good business sense no matter how you spin it.