iTunes music accounts for 70% of legal music downloads.
Size does not matter when defining a monopoly. Monopolies restrict trade. There are many services that are actually equal in price or less than iTunes with similar catalogs. Definitely not a monopoly.
Also, just because one part of the business is a monopoly doesn’t mean that other parts of their business are monopolies.
If they were to put Rhapsody out of business that would qualify as restricting trade, no?
No, the mere possibility of restricting trade makes a "monopoly". Actual restriction of trade is "abuse of monopoly".