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.