I'm not surprised.  Truespace has been around for ages.  People recognize the name, and download it to try it.  Maybe they had it back in 1998 or so, and are curious about new features.  The download rankings don't mean that people are actually using it more often than some others for that reason.

I'm really not surprised about Blender being 1st either.  Free is free.  They download it out of curiosity, load it, struggle with it's wacky interface for a while, then get some real animation work done in Maya, Max, or XSI.

Just kidding of course.  Maybe.