Just a minor point... if the RIAA were indeed a monopoly then there would be "some smaller label that is not part of the RIAA". They are without doubt powerful and megalithic but they are not a monopoly. Not in the legal sense anyway.
Not entirely true, Mr. technical.
From wikipedia:
In economics, a monopoly (from Greek monos / μονος (alone or single) + polein / πωλειν (to sell)) exists when a specific individual or an enterprise has sufficient control over a particular product or service to determine significantly the terms on which other individuals shall have access to it.
I think this is the case for music. The RIAA definitely has sufficient control to significantly determine access to it's industries product. They can easily squash out competition from smaller labels. I believe they can be considered a monopoly in the current market.