Comment Yes, the L4D2 content WAS promised for L4D1 (Score 3, Interesting) 130
http://ve3d.ign.com/articles/news/41219/Left-4-Dead-DLC-Promised
"Chet Faliszek said that Valve plans to get the DLC rolling much more quickly with Left 4 Dead than it has been able to for Team Fortress 2. Plans already in the works call for new campaigns, weapons, and boss infected (the game's zombie enemies). In addition, there were strong hints at a flamethrower coming not long after launch."
Yes, the valve team promised L4D 1 content, including new special infected AND weapons AND new campaigns. Turns out they saved all that for L4D2 instead. L4D2 will have a new special infected (charger), new weapons, and new campaigns. And no, they didn't add any new campaigns in L4D1, just tweaked versions of the old ones for versus, and a single new mini map for survival (the rest of the survival levels are just portions of the old maps in old campaigns)
That same guy at valve in an interview said they have been working on L4D2 since the launch of L4D1.
http://www.shacknews.com/featuredarticle.x?id=1138
"Shack: When did development on Left 4 Dead 2 start?
Chet Faliszek: Pretty much after Left 4 Dead launched."