but a core and critical functionality of your entire OS such that any
    attempt to sidestep or evade it would be met with ruination?

Was Internet Explorer ever actually a core and critical part of Windows? Sure, Microsoft claimed that it was. But of course, they would have done that, given that the alternative was to admit that the Justice Department's argument was correct, and that Internet Explorer was being bundled in an anti-competitive manner to deprive Netscape of sales.