Yes, you can buy what look like good spec pre-built PCs these days for about the same money as you could build them yourself. However the majority of the time they have cut corners. Often the motherboards are limited in some way, or other things like the ram, PSU, case or HDD are a budget make. They have to make a profit somewhere within the PC they are selling.

I still prefer to build a PC myself as I then know all of the components are qualiity known brands and also that the system has been put together correctly and how I wish.