Valve is one of those companies that won't release anything if they feel its below their standard. Which is awesome, but it comes at the cost of release dates being placeholders to the point where a game might not see the light of day (half life 2 episode 3 for example). Until you see commercials and a big marketing push for Left 4 dead 3 I wouldn't believe anything. also you might want to note that 360 will probably be the gimped version of this game as steamworks isn't allowed on it and Valve is really loving some steamworks on PS3.
As for Fallout 4 don't expect anything solid for atleast another 2 years. Skyrim is a huge project for them and I am sure they are all stations manned gearing up for its launch and the inevitable slue of patches that will have to hit post release. The tech and tools they built for Skyrim will probably become the foundation of Fallout 4 meaning you should see a vastly different game then 3. Fallout 4 PS4 isn't out of the question at this point.