My take
As long as their OEM contracts are protected under NDA, all they'd have to do is publicly claim that the OEMs are free to install what they want, then indivisually contract with each one to not actually do it. Thus the only way to ensure something gets installed is to require them to install it themselves.
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Microsoft offers them the one thing most business people will pay any price for - the ability to say "we had no choice - everyone's doing it that way." -- [link|http://z.iwethey.org/forums/render/content/show?contentid=38978|Andrew Grygus]