Permission to speak frankly? Alright...
PC Gaming is simultaneously the most casual and hardcore form of gaming. On one hand, you have Flash and Facebook games that require about 2 seconds of prior investment before playing. On the other hand, you have these technological behemoths of games. The problem the PC has is the uncanny valley between.
Most PC users (not gamers) don't know shit about their video cards, available memory, or any of that. Therefore, the prospect of actually buying a PC game becomes precarious for the noob. Either they edge away from buying a top notch game, or they buy a game too advanced for their system, and need to buy a part or two later on, delaying the fun. This is deadly for PC developers, forcing them to focus either on a huge range of theoretically powered PCs or focusing on an existing market.
Consoles have the advantage of being clones. The Wii I got in 2006 plays the games I buy in 2010. This eliminates a major hassle, and makes the Wii therefore more attractive to a casual or only slightly serious gamer.
The same goes for PC controls. In theory, the PC has better controls than any system, combining a hyper-accurate mouse with a huge array of keys and possible controller support. The problem is, this is nearly incomprehensible for newcomers. Even the DS, with arguably the simplest controls this generation, has a touchscreen, four regular buttons, four arrows, a couple of buttons used for menus sometimes, a microphone, and another pair of buttons in the frikin back. Unless the PC game in question requires just the mouse, it can be truly incomprehensible.
I do not dislike the PC as a platform. However, I think the PC, by its very nature, is an exclusive system that drives away its own potential audience.
As for Nintendo's ability to innovate, that is a topic for another day.
