Normally I'd agree, except we then get this:
A PS4 costs $400 and comes out of the box with a controller, all required wires, an OS, and for a modest fee each year you get 12 free games and even better discounts on Sony's already good digital sales. In addition to the digital sales, you have a variety of physical retailers who sell used or marked down physical copies of new games. The system will last you for the next five years, likely without breaking down and will play a large variety of third party titles and first-party exclusives until the PS5.
Now, you have $400 to build your core system. It must last five years and be able to meet the minimum required specs for games to be released in five years, you must include the cost of wires, keyboard and mouse, controller (if desired), as well as the cost of the OS. Wait, let's be generous; Call it $550 for five years of PS+ bought during a Black Friday deal, and you don't even have to account for the 60 free games a PS+ user would use.
Have fun!