Oh yeah, and isn't there some piece of hardware that let's you connect a mouse and keyboard to a console aswell?
The current best way of using KB/M on a 360 or PS3 is via the XIM, though there are problems and expenses many are not willing to tolerate.
You can buy a premade XIM or build your own for the PS3 for under $40. It's easier on the PS3 because the PS2 to PS3 cable adapter is zero lag and cheap. On the 360 the only zero lag cable connector is the pricey XFPS, which is a complete KB/M adapter rather than just cable. Nothing beats the XIM though for the adapting itself, so it's well over $100 for all the parts necessary for adapting the 360 as best as it can be done.
However, even the best of KB/M adapter setups are only as good as the game they're played with. Most console games are written exclusively for the analog mini toggles on gamepads. A scant few work well with adapters, usually the ones like Halo and CoD 4 which have a more flexible control scripting. So I ask you, if you were a PC gamer that struggles with gamepads would you want to buy a 360 then spend well over $100, and I do mean WELL over, just to have a hodge podge of parts that only get you good KB/M adaptation on a scant few games?
On the other hand, if ALL console games were developed like Halo and CoD4, it could very well mean even less PC game sales and more KB/M adapters would no doubt be made, dropping their price. The evolution of the gaming console has greatly complicated gaming for PC gamers, esp those whom detest gamepads. However, if say the PS3 were to get a more Wii-like controller, though more refined like the In2Games Fusion, I could see myself getting a PS3.
Even then though, it would only be if all games written for the PS3 made full use of the controller, including being able to point the device to aim, vs using mini toggles to aim. Mini toggle aiming is the single most thing I hate about gamepads. BTW, by more refined I mean the Fusion uses ultrasonic technology whereas the Wii only uses RF. The Fusion tracks so precisely it's not unlike blue/green screen CG effects used in movies.
http://www.engadget.com/2006/10/20/in2games-fusion-controller-spices-up-next-gen-motion-sensing/