Geoff Keighley made a clarification about one of the far reaching statements in his making of Portal 2 app "The Final Hours Of Portal 2" on the app's website today.
Source: http://thefinalhoursofportal2.com/blog/finalhours/welcometotheblog/Geoff's App Website said:Dan asks, At the very end of the article you write that Portal 2 will probably be Valves last game with an isolated single-player experience. Was this based on reading general industry trends, or something specific you heard from Valve?
Geoff Keighley: Good eye! This is coming from Valve, although I dont have a lot more to share other than what is in the story. I agree its a provocative statement, especially given the amazing single player storyline in Portal 2. Keep in mind Valve said probably, so I get the feeling that this could change.