Is money tainting the plasma supply?

Andrew Pollack's New York Times article "Is money tainting the plasma supply" (December 5th, 2009) fails to properly describe the notion of equilibrium price in the market for plasma donations.

If there is a cartel, it is likely to be tested over the next few years because after several years of rapid expansion, plasma supply seems to have caught up to demand and could soon exceed it.

One sign is that in Eagle Pass, payment for two weekly donations has dropped to $60 from $80 earlier this year.

In fact, the resource of plasma is being supplied by donors to demanders.  In this case, the demanders are plasma companies.  The price of plasma donations is found at the point where supply meets demand.  Without market distortions caused by, for example, government intervention, demand can't "exceed" supply (so long as price is free to adjust).  The curves are totally unrelated to one another (click to enlarge):

In addition, it is possible that a decreased price of the (alleged) plasma cartel's inputs likely signals that the cartel has gained in strength.  Generally, cartels and monopolies produce at lower quantities than the equilibrium described above: they restrict quantity in order to reap profits from a higher price.  However, a restriction of quantity would also imply lower demand by plasma companies for plasma resources from plasma donors.  Thus, a price decrease at the input level would be perfectly consistent with cartel behavior.  In order to claim that a cartel is losing power, it will be at least necessary to show that plasma quantity supplied by plasma companies has increased rather than decreased.