Microsoft and Intel have "monopolist" tendancies. One of their standard methods of attacking the competition is "embrace and extend", they appear to support an "open" or industry agreed standard - then add new features (which are *their* exclusive Intellectual property) and close out the competition.
ARM because it has many licensees can't be seen to discriminate against one over the other - so that ARM's standards generally are available to all and embraced by most. If Intel start adding Intel specific bits to the ARM standards that may "lock" companies into only using the Intel variant and gradually close off the competition.
All of this *does not* relate in any way to an "Acorn vs Microsoft/Intel" argument but rather to the broader notion that computer manufacturers should all compete fairly.