Re: "admitting they made a mistake is what keeps Windows firmly entrenched"
Sorry, but I cannot agree.
What keeps Windows so firmly entrenched is the fact that 95% of the market have been using it since it started, and are so used to it that they cannot change. That is why TIFKAM was such a disaster - it went against user habits.
It is for that reason that Microsoft keeps so strongly away from "rebuilding from scratch". The only thing that keeps Microsoft on the market is the fact that their OS remains compatible with legacy applications.
The day that compatibility dies is the day Microsoft folds, because companies - especially the Fortune 1000, are very ready to change for a free OS if they have no choice. So Microsoft stays compatible with legacy so as to give them no choice.