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So it's no longer even an issue of "good". MS software could be total junk, but people would continue to use it because their market share has reached critical mass. There is, quite simply, no way of surviving in business unless you run the same MS software as everyone else.
That is why people buy MS software. Because it is no longer really a "choice". For the majority of businesspeople (and others), it is a "need".
Sure, I can CHOOSE to run Mac OS X, or Debian GNU/Linux, or Gentoo, or FreeBSD, or whatever-- but when a client expects me to work with Windows-only stuff, then what? I either buy MS software or I lose the client.
The only "choice" left in the computer world for most (not all-- but most!) users, programmers and systems admins nowadays is "Run Microsoft software, or lose your job."