Ok, I'll bite: what makes you say that? I went to Apple's website and built an iMac. It cost $2000 with no upgrades. I went to HP's site and built an similar computer. $1,149.98, including HP's overpriced monitor that I could buy elsewhere for less. Oh, and I got a free upgrade in RAM, so the HP actually has better specs. And HP's optical drive is faster.
I think Apple makes some slick computers, but I'm just not sure how you can say they are comparably priced. Heck, with an iMac, you have to buy the most expensive one before you even get a quad core processor. That is seriously lame. I bought my "bargain basement" HP, as you call it, for something like $650 and I got a quad core processor.
In what way is that HP tower an all-in-one form factor computer? You are not comparing like to like computers at all. You are not providing any information at all on what components, specs on the monitor or its capabilities. Is that monitor capable of 179º viewing??? I sincerely doubt it. You said you "built" an iMac with no upgrades? How do you do that????? You either buy an off the shelf iMac or you build one with upgrades. You don't have it both ways.