It strikes me that Microsoft is playing a word game typical of progressives.
They’re trying to make it seem as if they mean ‘security’ as in, secure from viruses, or spyware, or pick your security related topic.
What they’re doing though is quite different. They’re making machines specified so that they are “Secured to only boot windows”.
They could easily open source this technology if it wasn’t the case, so as to prove that they aren’t purposely trying to lock out the competition.
That's been their MO since I can remember.
Of course, it helps that they were founded by a couple of huge liberals.