You must not look at the right places.  I can build any kind of computer I want.  Quiet, gaming, HTPC, small form factors, servers, etc.  I can buy pretty much every part from Newegg or Amazon and still come up way cheaper than buying a prebuilt from Dell, HP, Sony, Gateway, etc.  I'll even end up with higher quality parts and better warranties when building my own!

There are literally thousands of fan options available to find the quietest/best fans.  Thousands of cases available to find the quietest and best form factor for your needs.  Building is still the cheap option and the ONLY way to get exactly what you want in every way imaginable.

No, you can't just build an iMac with off the shelf components. Everything is crammed in there like sardines. The boards are custom to fit the parts in the minimum of space. Show me a case where everything fits into a 1 inch thick space, including the monitor, which requires no cooling fans that I could put together in less than an hour.

Also, I don't have time to spend hours and hours to spend building computers. The majority of people don't either. I've put computers together before, it just isn't even close to being worth it anymore. I have no enjoyment in building computers, it's about as fun as cleaning toilets to me. I'd rather spend my time doing something I enjoy.

Now you are in the realm of stupidity so let's leave it there.

However the Mac, Ipod, Iphone and Ipad are all powered by OS's from the same code base (i.e. MacOSX, the same OS), while MS wasn't able to port their OS to different platforms. They uses Windows CE for portable devices and Zune, Windows NT for Desktops and Workstations, a custom OS for Xbox, while the Windows 9x branch died almost a decade ago.

Oh no, so you found one example of something that can't be done with custom builds.  That eliminated like .00001% of the potential custom builders!  Darn!

You are clearly not a PC building type to begin with.  Not even the PC type by the looks of it.  Millions of people build their own computers each year.  The custom PC market and build-yourself market keeps getting bigger because it will always be cheaper and is the only way to get what you want.  All it takes is a few hours on a free afternoon to build your first computer.  After that it is all the same, basically, and only takes an hour or 2.

Can you pick any graphics card or memory you want from any manufacturer and swap it out at will in your iMac?  No?  Shame.  What can you do when your iMac gets outdated?  Can you re-use the screen, the casing, and just update parts like CPU, motherboard, GPU, HDD, RAM, etc?  No?  Shame.  Looks like you're stuck just buying a whole new iMac and wasting even more money every 3-5 years.  Apple is pretty much the worst when it comes to locked down, proprietary hardware design to keep all the upgrades and repairs restricted to Apple certified technicians.  Especially their iMacs.

Most people love creating their own items for use and being resourceful with gaining knowledge and experience at new tasks.  They especially love saving money.  Then you have other people who just buy it premade and don't care about costs or aren't technologically inclined.

Relax. Take a deep breath. Nobody is knocking system building. It's just not something that the majority of people want to spend their time on. The cost advantages were great 10 years ago, today not nearly so much.

Yes, there are millions of people who like building systems and all the power to them. But there are probably billions of people who don't. Neither is better or worse, just they have differerent requirements and desires.

Choosing something different, just to be different, is always in the realm of stupidity. That's the point.

Oh no, so you found one example of something that can't be done with custom builds.  That eliminated like .00001% of the potential custom builders!  Darn!

You are clearly not a PC building type to begin with.  Not even the PC type by the looks of it.  Millions of people build their own computers each year.  The custom PC market and build-yourself market keeps getting bigger because it will always be cheaper and is the only way to get what you want.  All it takes is a few hours on a free afternoon to build your first computer.  After that it is all the same, basically, and only takes an hour or 2.

Can you pick any graphics card or memory you want from any manufacturer and swap it out at will in your iMac?  No?  Shame.  What can you do when your iMac gets outdated?  Can you re-use the screen, the casing, and just update parts like CPU, motherboard, GPU, HDD, RAM, etc?  No?  Shame.  Looks like you're stuck just buying a whole new iMac and wasting even more money every 3-5 years.  Apple is pretty much the worst when it comes to locked down, proprietary hardware design to keep all the upgrades and repairs restricted to Apple certified technicians.  Especially their iMacs.

Most people love creating their own items for use and being resourceful with gaining knowledge and experience at new tasks.  They especially love saving money.  Then you have other people who just buy it premade and don't care about costs or aren't technologically inclined.