When people say "oh, the PC is full of random components whereas the console is specialised", the key is Windows. On a PC, Windows basically sits between anything you program on it, and the hardware itself, so that it can interpret what you're wanting to do, and customise it to whatever your hardware is, so that it actually understands. And of course, Windows has all those other little extra functions like multi-tasking. That kind of functionality does of course lead to a fair bit of performance loss.
On a console, you're right in there with the components from the start. When a game tells the 360 to draw a bad guy, it goes straight to the graphics card and does it (in a sense).