Whoooops. I accidentally put “I don’t think this would be a nice option” when I really meant for it to say “do” think this would be a nice option and was just in agreement with sausages. Edited my original.
I posted a script a while back that would remove all verts with very low weights from vert groups. The third script in the post below is the one that might be pertinent here.
http://blenderartists.org/forum/showthread.php?t=112969
may I ask you why it matters so much for you?
Does it affect performance or some other matter ?
I really don’t know so I am asking.
I’d say the main reason it can be a problem is that vertex groups have other uses besides weighting. For example, they are used for selecting. If you have a bunch of near 0 or 0 weighted verts in a vertex group it becomes useless for selecting vertices.