Your comments are not insensible or uncalled for but it does show an uninformed opinion about how most people do their computing.
It is possible to build yourself a car. All the parts to make one whole car are available for sale over the counter or over the Internet.
http://photoblog.nbcnews.com/_news/2012/08/31/13588649-homemade-lamborghini-replica-draws-admiring-glances-from-chinese-drivers?lite
It is just that very few people are inclined to build their own car. Too bothersome for a lot of people to do. Most consumers prefer to buy a Dell, HP, Lenovo etc etc and even an Apple. What sets Apple apart and not just another commodity item is the software and hardware design that is exclusive to the company. Thus they can charge more.
As for cobbled together desktops these are in decline and eventually be niche for DIYers and gamers. As for their out of the box counterparts these are also in decline yielding market share to mobile devices like notebooks, tablets and smartphones. I am not saying that you shouldn't be doing it but for most folks they just want to open the box, plug it to the wall, turn it on and start using it. Then completely replace within 2-5 years.
To make ever smaller and lighter computers manufacturers must solder parts together. This is the direction Intel is planning to take eventually by 2015.
In terms of supply chain cost desktops are much more expensive to move around and store because they take up more space and weigh a lot more.
I know everyone wants to save money on a deal so why aren't most people using m43rds and not SLRs? 
I do apologize, my comment that you referenced was insensible and uncalled for. I definitely agree that those luxury car brands overcharge for what you get, but I see it slightly differently just because it is not possible to build yourself a car. If you want that sort of performance or luxury in a car, there is no (street legal) way around it. Unless I am forgetting something, then do let me know if that is the case!
I did exactly what the OP was trying to avoid, incite an apple vs pc debate. For that, I am sorry and will not make any future comments regarding the electronic rivalry. My intention was to ultimately convey some information about the iMac architecture and that alternatives do exist if money is a concern. BTW, If anyone is looking to build a computer and would like some help, I would be happy to do what I can!
I am well aware of the attempts to replicate expensive exotic cars or even build tuner cars from kits (such as the ultima gtr720) that purely built for handeling and speed. Most of which are not street legal in the united states and have little practicality in the real world. Given that these are so different than luxury cars such as BMW, mercs, audi, etc., I still do not think the car example relates. On a side note, I build go karts for fun. They are definitely not street legal, the interior doesn't look anything like a 750LI, but damn it can drift around a turn. Not so sure I would be willing to do that in a $100k bmw haha. But hey if my go kart was street legal, I would drive it everywhere!
Anyhow, I build computers for fellow engineers along with people doing 3D rendering, audio engineering, video editing, etc. I guarantee you that computers are not just for the gamers and those who feel like giving building a try. In the custom computer world, home built computers utilizing raid controllers to control the flow of data to SSD's and overclocked processors have overpowered the 5k+ custom ordered computers from dell (or hp i cant remember). When professionals request a custom build, they are set up in such a way that factories cannot meet their expectations or would charge insane amounts to do so. That is the driving force behind why I build computers for others (i dont charge for my work either because I enjoy it too much

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I actually know quite a few engineers who work at intel (a major intel facility is just 20 minutes from my house) and are very knowledgeable about the 14nm integrated processor architecture. This is the way of the future, but is not going to cause custom build computers to cease to exist. Intel makes far too much money from the custom pc world to risk that. But it also will have a profound effect on advancing major computer companies (dell,hp,etc)
I realize 95% of the computer market is just looking for a computer to turn on an preform basic tasks. I just find it astounding when they spend twice as much for an iMac than a custom build that I recently did for a client that has 2 to 3 times the processing capabilities. (not just the processor alone - this takes into account overclocking on the processor, ram, having an ssd raid array, motherboard to handle the sensitive current and high data flow, etc.) In the end, all that matters is how many floating-point operations per second is achieved.
But hey, if owning that beautiful aluminum computer is what makes you happy, more power to you