That doesn't really change the point much, does it? Installing your own non-Windows OS on a machine is a very small part of the market. Providing security for the people who will never install a new OS on their machine (not even a new version of Windows) is serving a much larger part of the market.
Providing security for the much larger part of the market does not mean, that it is necessary to lock out the minority.
Otherwise, why have the antitrust laws at all? The dominant market players provide useful services, why should we care about the minor players? (Not only in operating systems, but in general).
