Oh and the reason for the decline of PC gaming is very obvious:
The PC is accepted in the living room nowadays. We don't want to head for the attic any more to our Geforce 9800X2 tower. But only as long as it comes in the form of a laptop or as a gaming console. Guess which of the two sucks at gaming 
And the wide living room accepted iMac sucks at gaming too.
I don't know, I've seen PCs hanging out in living rooms since even before anyone knew what an "internet" was. Conversely, I still prefer playing PC games in my room (not out in the open). PC games, with few exceptions, aren't really social (with people in the same room). I don't think the "decline" mentioned in the article was for any terribly significant reason other than some more-than-likely obvious catalyst for the decrease (e.g. lower 360 price, explosion of Wii, wife feeling amorous, etc. ).
Uh... most PCs in the living room are usually there for a technical reason. In ye' ol' days of dial-up, this was usually where the phone was located. Rather than just install more phone jacks throughout the house (my friends would express surprise at a phone in the bathroom... they didn't really understand my dad), most just put the computer nearer to the phone. Now, it's where the cable broadband would be located, same reasons. It's really strange to come across so many homes that don't have cable in nearly every room. The other reason is for parents to try and prevent their kids from looking at porn.
The "decline" is just a line of ---That which is odiferous and causeth plants to grow---. It's a pendulum. For a few years, everyone will say PCs will be on the decline when new consoles are introduced. Then people will say consoles are on the decline as consoles reaches the end of its useful life and new PC hardware is released. PCs have their place that can't be filled by consoles and vice versa. It'll be a long time yet before that gap between PC and console is fully closed, if it ever closes.