Valve's Erik Johnson says they "don't have a ton of experience" in their teams for developing on other platforms, "made a lot of sense" to stick with Xbox 360 and PC.
The team will "keep building stuff" for L4D 1, they aren't dropping patch and content support. To keep customers happy is "good business" so the sequel supports the original as well.
"We don't have a ton of experience internally building products for other console platforms. Left 4 Dead 1 was PC and Xbox, so it made a lot of sense to go for Xbox this time," Johnson tells Eurogamer in an interview.
"We're going to keep building stuff for Left 4 Dead 1. We'll support both. We've always felt that it makes good business sense to keep customers happy. It'll be good for Left 4 Dead 2 to support Left 4 Dead 1."
"We do have risks in that we don't want to split the two camps, we don't want a Left 4 Dead 1 group and a Left 4 Dead 2 group, that's a problem that we need to figure out."
Left 4 Dead 2 is being released on Xbox 360 and PC this November 17th.