I have imported the Aiko mesh into Wings3D to use as a clothes template. On applying new materials to the groups, I noticed some strange areas in the mesh. On other meshes the shoulder-collar boundary is usually a more-or-less straight cut through the limb. On Aiko there is this notch (see image). There is also a notch at the hip-abdomen boundary. At first, I thought it was a better way to set up for the blend zones but after studying it for a while I don't see any advantages. Anyone know why they made the grouping this way?

You obviously haven't looked at David, have you? This seems to be the new approach for Daz3D models' body parts. The reason may have something to do with JPs; best to ask Daz about that.

V3, David, Aiko, Steph Pet, She Freak, Luke, Laura ... all have the same faces split. Only M3 and F3 use other scheme.

It might be to make the shoulder look better when it is bent.

Grouping doesn't affect the way a mesh bends. Bloodsong's book has a fantastic example of the same mesh with the same joint parameters and vastly different slicing, and they all bend the exact same way. Of course, DAZ claimed not to know this and that's why M3 has different grouping (which also happens to break the morphs and force you to buy new sets).

That's a very good point (which Bloodsong makes very convincingly in the book). It doesn't affect JPs and it definitely has no material 'zone' usage. Makes one wonder...

Since there's no technical reason to do it, they might have done it as a way to catch mesh thieves trying to sell items on Turbosquid or e-bay. The non-functional grouping could be a kind of trademark in that way, something a stupid thief would leave in when he tried to resell the mesh under a different name, and get caught as a result.