TypicalSurfer - 4:50 pm on Aug 27, 2012 (gmt 0)
Sorry to beat a dead horse, but who are they discriminating against?
Discriminatory pricing simply means preferential pricing or other accommodations for some customers giving them an upper hand in commerce resulting in less competition. Auction based PPC by default works this way (hence the cover of "quality scoring").
Where it becomes an issue for regulators is when the effect may be "substantially to lessen competition or tend to create a monopoly in any line of commerce."
poke around for "Robinson–Patman Act".
I actually think PPC has morphed into predatory pricing, going from innocuous penny clicks to advertise a good or service to eating entire margins, eliminating smaller players. The end result is the same, lesser competition, less choice for consumers, basically a harmful practice (from a regulatory standpoint).