Sounds like we're talking about more than one thing here...

True soft-body effects would allow parts to deform on collision. That would be great to have, though I understand why it is no small request.

The games which were mentioned (and also the most recent Soul Calibur as well) use what has been termed "jiggle-physics".  I understand if some people think this is a silly feature, but it has been implemented already in games, so it's hard for some of us to accept that it couldn't be done also in Poser.  

IClone has spring solvers, which would be great to have in Poser as they could probably do a large percentage of what people are wanting soft bodies for.

http://www.reallusion.com/iclone/help/iclone3/11_Props/Spring/Spring_Props.htm

But they are not the easiest thing to set up, and I don't believe they can easily be added to a figure within IClone/3DXChange.

Sparrowhawke has a "Jiggles "plug-in for Carrara that would be great to have for Poser.  I'm not sure that such a thing is overkill for still images, as images created with it look much more natural than the same images without it.  Body masses are soft, respond to gravity and react with inertia.  Whether or not I could properly deform a body part with a magnet or morph, it's the gravity and inertia that are the problem.  Could they be keyframed?  I know I'm not good enough at animating to do that over the course of a lengthy animation.  That is precisely the problem we would like to have a solution to.

It's not just breasts, but also bellies, buttocks, antennae, ears, tails, and transmapped hair are difficult to animate without an automated  jiggle or spring.