I think this phenomenon is explained by a simple economic rationale:
Manufacturers compete on price, but have to control quality to a chosen fixed standard. For example, it's extremely rare to buy a new car that doesn't start. Cars are clearly quality checked for safety and their parts are made to last at least as long an the warranty. A company would lose money otherwise.
The final step is inspection of the completed cars. Each car undergoes strict inspections of 1,500 to 2,000 different things to make sure the brakes, windshield wipers, lights, and other parts work.
Only after the car passes all inspections is it shipped to the customer.
So, given a set quality, the competition is on price. Manufacturers will tend to use pieces that are good enough to last, but mostly cheap - cheaper than the competition.
Therefore, in a way you are right, using cheap parts they compete better so they make more money than otherwise - however I would say they are pushed by economic forces and not mere greed.
On the other hand, it just as clear that they use all available dirty tricks, like seriously overcharging for parts (one front lamp 400€?), in the after market. This is where there is basically no competition pressure.
The European Commission’s latest report on car prices shows that prices fell slightly, in real terms, in the European Union in 2009 and also converged within the EU's single market. At the same time prices for repair and maintenance services as well as spare parts continued to rise well above inflation confirming the need for the stricter competition rules in place for the sector since the 1st of June.