Kotaku got a hold of Gabe Newell (co-founder and managing director at Valve) about the community's concerns over the Left 4 Dead 2 announcement at E3.
"Doing a sequel in one year is new for Valve. But providing ongoing support for our titles after the initial launch isn't - it has been part of our philosophy since Half-Life was released ten and half years ago," said Valve president Gabe Newell in a statement to Kotaku. "We see no reason to change that and will continue to support the over three million customers in the L4D community."

"E3 is a trade event where developers and publishers come to announce new games for the coming year. L4D2 — like any new product — requires an appearance at the show," Newell said.
More at Kotaku...