Actually, this argument is a bit flawed... but rather than negate it entirely let me try to steer it in the right direction:
The logic behind it goes something like... the product is the distributed item. IT is not. The product is the music which is itself intangible. The various media in which it is fixed are tangible, but they're simply the method of delivery. It would be like arguing that if Ferrari increases their output to 2 million cars a year (exponentially more than present) that somehow the Ferrari design is worth about the same as a Ford, and Ferrari engineering is worth about the same as a Ford. Neither of which are true.
So now you have Artist A and Artist B. Artist A is a big star, not very talented, but a ton of money was thrust into their production and marketing. On a cost basis, their music is worth more. On an availability basis, their music can be argued to be worthless (because they sound like everyone else). But... there are STILL more people out there wanting Britney's albums than there are Britneys. Many times over. The record label can demand a high price for this artist's material, and expect to be paid it. Even if the value is low
Artist B is not very popular, and their talent is such that it is rarely found. Their production costs were low, since they recorded it all on a four track reel-to-reel, in one take in the bass player's living room (based on a true story... jazz trio I did CD mastering for had done it just like that). They won't ever see high demand, but their talent is rare, their music is very original (and therefore also rare), and so their value is high... but their price doesn't have to be in order for them to make a reasonable profit.
When it comes to dime-a-dozen pop stars, also consider that just like Coke, Pepsi, Big K and a bunch of lesser brands are absolutely the same, how often do people choose Coke instead? Why? Brand perception. Lots of money is put behind marketing a Britney as a brand unto herself. Even though she's utterly replaceable, the cost of creating a perception that defies reality are high and too must be recouped.... but they pay off in that they are often successful in creating that perception and therefore falsely inflating demand to counteract the broad supply of music like hers.
It also doesn't matter how many copies of Britney's latest album are crapped out by iTunes... People who believe that Britney is different will want Britney, and not the Kroger generic brand version of Britney, of which there are thousands.
But if you still don't believe me, may I ask what brand of soda you drink and why?