An interesting interview with Valve VP of Marketing, Doug Lombardi:
"But I think a lot of what's happening now in the public perception and the press perception is fueled by thing like NPD releasing sales data from retail in the States that says "Oh, PC games were only 12 per cent of sales at the holiday" - or last year, or whenever it was - and everybody grabs hold of that and all of a sudden declares that PC gaming is on the way out and what-not. But that ignores all the subscription revenue from World of Warcraft, which just by itself would change that number, that perception that's its only 12 per cent of the business. Just add that in and all of a sudden I'm guessing it's over 20 per cent of the business. Throw in things like Steam sales - that's going to move it again. Then there are different models, like the DICE guys are doing."