While I agree with your post in spirit I have to severely disagree on it's scope.
A Forza 2 driver using a 360 controller would absolutely ruin one that's using a keyboard.
You're forgetting that it's keyboard
and mouse. A mouse could easily mimic the analog control required for turning and acceleration. It lacks the tactile feedback of a thumb stick but a HUD indicating turning/acceleration position could give that same feedback. Since other graphical elements need to modified between consoles and PC I'd consider that a slight win for consoles.
All the keyboards and mice in the world won't let you play Smash Bros. 4-player in the same room.
This is solely a software limitation. There is no hardware restriction stopping someone from plugging in 20 USB keyboards and mice in to one computer and using them.
Consoles let you play more genres well than PCs do.
You're kidding right? I'll give consoles fighting and driving/flying games, but PC's keep FPS's, anything with a complicated interface (RTS's & MMO's & most God-like games (Sim city, dwarf fortress, etc.)), puzzle games (bejeweled and puzzle quest style because it's faster to click on something then it is to move the cursor and myst). Adventure games are a toss up depending upon the game's needs and design.
After all, if a PC game requires a USB controller to be played, I'm willing to bet good $ that it won't sell very well.
The market has proven that people will pay a decent amount for an extra controller with Rock Band & Guitar Hero. Granted that is on consoles, but there is no real reason why the same couldn't happen on PC.
In general controllers excel at multiple degrees of analog control (a mouse only has two while a 360 controller has 6) and simplified interfaces. While a mouse and keyboard excels at precision of analog control and sheer number of keys. Each one is better at somethings and worse at others, but it's a pretty even split. Though that may shift if Supreme Commander can get a decent interface on xbox and as games move away from text communication to voice chat and text to speech.