Hmmmm... they can either keep patching a game with minimal changes every few months, or make a new game each year that compiles lots of changes and enhancements.
I guess I don't see where the problem is as either approach works for me.
I do agree that just 1 year later does seem a bit early, but what if L4D 1 was just a trial for them in hopes of releasing a much better, more advanced, longer, et all game based on the feedback? If that be the case I'm glad I could help.
And seriously, how often do mass amounts of people play games online a year after they release? The only ones I can think of are scarce, especially on consoles.
Also, CoD has yearly releases that only minimally change the games, and do we boycott them?