And what if a pre-assembled PC is cheaper than your custom built PC by $300-$400 provided certain minor things are inferior to your custom PC?
BWAHAHAHAHAHAHA!!!!! Oh....my sides! You should have been modded +5 funny!
This never happens. Ever.
Businesses can buy components in bulk, at a far cheaper rate than the huge markup a typical customer gives to component makers when he buys individual components.
Ok, think about the market. Is the largest market segment high end or low end? The answer is low end. Vendors have a much easier time moving low end systems than high end systems, so they always bulk rate the low end in significantly higher quantities. The markup is lower, but they move a hell of a lot more of it. That's where the bulk of their profit comes from.
If you order a machine (via some configurator or something) and select a component that is either higher end or not something they're trying to dump, then you will pay a significant premium.
Go over to someplace like PC part picker and put together a machine for some budget. Then go to someplace like CyberPower and try and configure one with the same parts for the same price or cheaper. Even for low end you can put together a machine for at least $100 cheaper (and with better parts).
You also don't have to deal with malfunctioning parts because the pre-assembled PC has been tested.
You missed your calling. You should have been a comedian.
Perhaps you should go read forums about some of these vendors. DOA's. Foreign call centers. Botched RMA's. Runarounds. You're at the mercy of whatever QA process and team they had test these machines, then your at the mercy of whatever craptastic customer service they're running.
There are quality vendors out there, but you're going to be paying a premium. Good service isn't cheap and neither is good QA.
So it's not all black and white.
Yeah it is.
If you're fine paying a premium from a GOOD vendor, then by all means go ahead and do that. If you don't mind taking a chance with dumpster vendors or don't really care about getting the best value for your money, then go ahead a buy a prebuilt. But the best bang for your buck is going to come from building your own.