I don't understand the rules they are applying to compare topologies.  My feeling is that an efficient mesh for violin and sax would have vastly different flows; a sax would have edge loops around the tube, and a violin would have edge loops along the sides (aka in the orientation of the perfling).

Maybe they are comparing surfaces directly.  But that fails as well; a sax is topologically a donut (a tube with one open end, and the other crimped almost closed).  A violin is a box with two openings into the center void.  Okay...I guess I can see the topological inversion from one to the other.

But like you said, once you add the rest of the parts; valves, reeds, pegs, strings, bridges, et al, any similarity of the base shape becomes trivial.

So my best guess is the linked-to library has only six items, and the violin was more similar to the sax than was the Maserati or the aardvark.

A little further off the subject; I too have Hexagon and Carrara (and I've also tried C4d, Wings3d, and Amapi).  I find Hexagon too unstable for my tastes.  When you finally figure out what a function does is when the whole program locks up on you.  Carrara, in contrast, I find extremely intuitive modeling-wise, with an interface that I find friendly and easy to navigate in (as a comparison, I start yelling at Poser when I have to go back there and experience it's lousy camera controls again).

I'm in process of building a drum kit myself (doesn't EVERYONE build one?  That, and electric guitars....!)  The differences in mine are an excrutiating level of visual detail in some of the fittings, and maximum support for both posing and animation.  Finally got my pedal rigged for Poser so all the cams and belts and springs work correctly.  Now I have to do the same magic to get snares with working tensioner and throw-off.  Even put "hit" morphs on the drum heads.  It's a lot of work to get a fully functional musical instrument.

But there are two big problems to the process.  One is that it is very difficult to coordinate with the Poser figures using it.  It's one thing to rig the valves on a sax (you can even rig them to respond to a MIDI file!)  Quite another to get a Poser figure to finger the valves correctly, while swinging and bobbing.

The other is, as the Animusic people figured out, a lot of instruments aren't that exciting when animated.  Many don't really change shape at all when sounding.  So if you want exciting animation you have to leave realism a little and put in morphs for how the sound "feels."  Max Fleischer horns, et al.