Yeah well there is more to it than that, but the competition helps drive prices down you are right. At the same time though since there are so many other companies that design and manufacture hardware, you are getting hardware from the lowest bidder in your HP or Dell.
Apple designs all their hardware themselves. They have their own engineers designing their circuit boards from ground up. So, the cost is more to begin with. Where as HP or Dell use hardware that is designed by someone else and the lowest bidder gets the bid.
I will also go as far as to say that in most cases by design one motherboard is not that different from another physically speaking. its design is definitely different. Which can have an impact on performance overall.
I am just saying that there is more quality control gone into making a Mac computer so the it costs more to make it, and they need to make their money so they charge a bit more to make their money. I used to work for an AASP several years ago, and I saw the wholesale cost of apple computers and the mark up isn't all that great and is comparable to PCs easily.
Sure you get tons of choices and that may be a huge factor but at the end of the day most people just want their computer to work.
As for desktops go, I fully agree with you. I build all my desktops and buy older (cheaper) Mac ones. I have a dual 500 G4 and a dual 1.25 G4 MDD desktops at my home. They still run OS X fairly quick and fairly well. I don't know any PC that is 4 to 5 years old that can run Vista. That kind of says something in my mind.
I am not bashing PCs because I like them as well. I use XP and Linux, but refuse to use vista at this point in time, and for the most part I like my windows machine. I just don't try to say that Macs are too expensive because you are getting more of a computer for your buck in reality.