The quotations say nothing of the sort. A vendor could provide a dual-boot device providing they have an Android bootloader signed with Microsoft's signing key, which is a service that Microsoft will be providing. A more open question is whether any of the existing Linux vendors will be doing this. Fedora is willing to use Microsoft's signing service for x86 because users will be able to disable the feature or enrol…
edit: I'm sorry to see the child comment downvoted. I am under the impression that user key enrollment is disallowed, but I'm actually not seeing an mechanism by which Microsoft can prevent the signature of ARM based bootloaders.
That having been said, I don't completely understand ARM devices to know if it's plausible to sign an ARM bootloader with the MS key.
edit2: The person y'all downvoted is the guy who wrote the blogpost outlining the Fedora way of handling this issue: http://mjg59.dreamwidth.org/12368.html