I'm pretty sure there's more than just The Next Penelope on Steam. Shouldn't Insanity's Blade, Airscape: The Fall of Gravity and Cosmochoria be on the list as well? Those last two are actually promoted on the Construct 2 Steam page!
Yes, those games are on Steam but they got there through Steam Greenlight.
Tetriser is only listing non-Greenlight games and provides a link to those on Greenlight. The Next Penelope is the only one (that I know of) that made it on to Steam without going through Greenlight.
If Tetriser listed all the games that were on Greenlight, there would be well over 100 games in the list and a good proportion of those have gone on to be greenlit and released.
For a list of C2 games on Steam Greenlight click here