A good part of that is marketing and business strategy. Its a lot of work to develop a figure mesh that bends and animates properly, so if you - as a business - can find a way to reuse and resell the same mesh and just put a different label and packaging on it, it saves that business a lot of time and expense that would be spent on developing multiple meshes.  But the plus side to it is that savings allows for these figures to cost the end user much less than it would otherwise.

But with that said, just about any mesh can be made to look like a completely different figure if enough time is spent on sculpting it and the mesh can support it. 

With Poser it's a bit different (or at least it was before) due to the grouping and rigging that cause limitations to body shapes and sizes. With weightmapping and animated joints, and now better scaling, it should be much easier to make one poser mesh look like 10 very different people if that's the goal. As long as the mesh has enough geometry to support it, and I'm not talking about SubD. SubD has its uses and benefits, but it's no substitute for geometry because it can't add edgeflow that isn't there to begin with. It can only divide what's already present. 

There's also the added element that each artist has his/her own style, and that style is going to be obvious to anyone that's familiar with the artists work. Since most of the character sets available for V4 are all based on the same morph shapes, (created by the same original artist(s) they're all going to look relatively the same. But look at some of the completely custom body/face morphs out there, by artists that didn't use morph sets, some of them you can't tell at all that it's a DAZ figure unless you look at the mesh. 

Personally I think it adds consistency and a more professional look to a scene when all the characters look like they were created by the same artist. When there are multiple figures from multiple artists/sources in one scene it just looks bad, more often than not, and starts reminding me of that VH1 show from a few years back, Drawn Together.

Plus you also have to consider the diversity of content, which would be even more limited if every figure had to have its own wardrobe. People would still choose one figure or body shape to support and that one would be the one that had the most content available. 

However I don't think male and female figures should use the same mesh. The male and female bodies are too different to pull it off well in most instances. If there's enough geometry there for shaping then it's fine, but with this trend of trying to make every figure 10,000 polys or less (for no logical reason with todays processing power), male and female shapes are much more difficult to make believable from the same mesh, so it's going to look either too feminine or too masculine.

That's my take on it anyway.

 

~Shane