Erik Johnson from VALVe confirms in an email message to a fan:

We’re planning on adding achievements to all of our games you touched on in your mail. We’re just now coming out of the post-shipping haze, so these should start showing up on Steam pretty quick here.

We’re also planning on adding a bunch more to TF2, starting with an achievement pack for the Medic in the next week or so.

Erik

Kudos slugz on steampowered forums.