It is unethical for Microsoft to use its monopoly power in the marketplace to dictate to its partners what they can and can't install on the computers they manufacture in order to protect and enlarge Microsoft's monopoly power. Apple has no monopoly power in the marketplace and is not threatening anyone who refuses to install Safari.
What Apple is doing here is merely annoying. However, I do think that when Microsoft was found guilty for the umpteenth time and got away with a slap on the wrist, Apple noticed and decided to play a bit of hardball, too.
As has been pointed out elsewhere, Apple's gambit is designed to loosen Internet Explorer's grip and make Microsoft's version of the Web the same as everyone else's (and not the other way around). I think that's a laudable goal.