Actually, Introversion's games were on Linux before even the first Humble Bundle existed, which made the later Bundle appearance a bit of an outlier in that department.
The real surprise in the list is The Book of Unwritten Tales, which I think is the only non-Valve/non-Croteam title in the catalog that was not available on Linux before today. And in its genre (traditional graphical adventure) it's a very high-profile title.
Not bad at all for a beta start. There's a fair amount of good games inside there. I am not in the closed beta yet, so I have no way to say if this work but I certainly hope to try this soon when they open the beta. I wonder if they are still expecting a 2012 launch or whether the actual launch timing is going to be pushed back to 2013. The later is more likely.
You'll notice that Crusader Kings II gives a "no files" error when you try to launch it from the library (you have to own the game already). When I posted this as a bug I was told that CK2 was in an invite-only closed beta. I guess that means I have to get an invitation from Paradox.
I'm assuming the rest of the games with a "no files" error are still being tested or prepped for release.
That's awesome. Of course many of these were available before. But having a good selection together in Linux under the Steam brand is a huge deal. If you're bored, chances are you can pick up something there in a couple of minutes. Chances are, you already have an account.