You keep using that word. I do not think it means what you think it means.
Exactly what does Apple hold a monopoly over? Mac OS X? Apple iPods? Or maybe machines based on the A4 processor? Even in areas that Apple is one of the strongest, such as music sales, portable music players, or smartphones (even though that is just a subset of the cell phone market), there is still plenty of healthy and growing competition.
New systems generate new problems.