All snarkery aside, I really fail to see why people are complaining about the lack of extras.
The Sin City DVD I also got had almost no extras. I was really jones-ing for a Rordriguez/Miller commentary track, with maybe a bit of interjection from Tarantino (although there is no such thing as just a *little* bit of interjection from Tarantino), and there was nothing. A brief Making Of featurette and that was it.
So I'm happy as a pig in Congress with the Serenity extras. At least I get a commentary track outta Whedon.
But still waiting for that Special Edition Naked Fillion boxed set...