I agree.
When your marketshare is that big you have to be more careful than everyone else not to abuse your monopoly, but you can have a far lower marketshare than that, less than 50%, and still get nailed for monopolistic practices.
Can you give an example of a company with less than 50% of the market getting "nailed" with monopolistic practices. One of the tests for such judicial involvement is SHOWING that the defendant company is in a monopolistic position. Having less than 50% of the market would be prima facie evidence that they were not a monopoly.
British Airways, explained in post #57.
Numbers don’t matter so much as leveraging what power you do have in an anti-competitive manner. Of course the bigger the numbers you have, the more power you tend to have, so such practices tend to be found in the 50%+ group.
For example, Apple is acting in an anticompetitive manner against Psystar, trying to not allow competition. Yes, I know the judge denied that. But their monopoly is a legal one based on the limited granted copyright monopoly Apple has on OS X (the extent of said monopoly still to be decided).
It’s like if you invented a revolutionary optic mechanism for a rifle scope and sell a scope based on it. You’re a small part of the market, but 100% of the market for scopes with your mechanism. Your patent on it keeps out the competition legally. BUT, if you manufacture and sell that part, you can’t keep others from making scopes based on it (your rights were exhausted at the time of sale as with, IMNSHO, copyright). Selling the part but still trying to keep others from making competing products is anticompetitive.