A Fel-Pro headgasket kit is $98 for a 2.0 DOHC engine. Fel-Pro is top of the line in terms of parts. Even an honest repair shop would only charge $130 for that. A dealer selling OEM parts will be marked up like crazy, and really the quality is no better than a brand name product. Many times the aftermarket is better.
Mopar has a value line, its basically over priced parts store replacement parts with their logo stamped in.
I pushed this thread off topic but what the hell :D
What you said is true and also not as true (personally I have no problem putting Fel Pro stuff on anything I own as they are a supplier to many of the world's OEM's). A lot of what manufacturers sell is just supplier / parts store stuff with a nice box. Example, I found out who the OEM supplier is for Volvo cartridge filters for my car (MANN) and bought a case of them for half the price of the nice blue box. I work for a fortune 50 company and have access to purchasing data. I know for a fact that some of the parts purchased are just catalog type parts, marked up and put in a shiny box with our part number on it. As you said, there are many aftermarket products that are better than OEM. I flushed the brake fluid last year on the same Volvo but instead of using OEM fluid I used Motul fluid. Similar price, higher performance.
The tough part is knowing whether a parts store item is the same, better, or worse than the OEM stuff. For example, I won't touch parts store water pumps, power steering pumps, alternators, starters, rebuilt brake parts unless its an emergency. This is based on the fact that many of the major remanufacturers piece together used parts to make their stuff work, or worse, use crappy third world country replacement parts that don't meet original spec. Of course some of these could be better than the OEM stuff, especially if the Ford's of the world have changed suppliers to save a buck. But really hard to know.
Additionally, sometimes the parts were designed to a certain spec and the replacement parts manufacturer missed a critical point when they went to manufacture a replacement product. Example, the glow plugs on 6.9 / 7.3 International / Ford diesels. You have to use the OEM or better glow plugs. Autolite has (or used to have) a reputation for good parts but their glow plug tips swell if the glow plug controller sticks, which means that the ends either break off when the glow plug is removed (bad... have to pull the cylinder head) or break off while the engine is running (really bad). In any case, that's why my line of thinking is OEM, always, unless there is a known better solution.
Just to add a little more fuel to the fire, tires are starting to become designed to a particular manufacturer's spec. There was an article in one of the car magazines a month or so ago that went through it. Not just the Ferrari's of the world either, Hyundai, BMW, and I think GM and Ford all have their own spec that makes the tires different from the same exact brand / appearance as an off the rack tire. But they aren't the same (that being said, this does not bother me at all).
Just my $.02. Not begruding the parts stores in the least. I have accounts with them and they know me by name. I just am particular about parts for the reasons above because I try to keep my cars exceptionally clean / well running and performing. 98% of people are probably going to be ok with parts store stuff for all their needs.