I think a good way to describe it is... when you use a Poser Magnet (with default fall-off curves), the strongest effect is towards the center of the magnet zone, with an nice, smooth transition (of less and less effect) out towards the outer edges of the magnet zone/sphere.  So the vertices on the outer edges do in fact move 'slower' than the ones in towards the center, but it's a smooth movement / even distribution / proportional movement overall.

Now contrast that with trying to replicate a similar morph by re-positioning one vertex at a time in a modelling app.  You might end up with the same general shape, but chances are that you'd have a hard time getting as smooth/proportional movement (of course most modelling apps have soft-selection tools and other deformers/tools that serve the same purpose).

EDIT: I haven't used it much yet myself, but I'm pretty sure that the Morph Putty tool in Poser also does soft-selection, for the same purpose.

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