Wasn't it Christopher James Huff who wrote:

>Vertex normals aren't perfect in all situations either. Consider a cone 
>formed of a fan of triangles. Each triangle has only one vertex at the 
>point of the cone. You will have as many normals as triangles at that 
>point, and no interpolation between them...

There's no reason why a mesh can't have several vertices at a single
point in space. Modelling programs split vertices at places where
there's a discontinuity in the normals (like where the side of the cone
meets the base) and the same thing can be done for the apex of the cone. 

If the cone mesh is uv-mapped, then the apex point has to be split into
multiple vertices anyway.

I had a quick look at a cone object generated by Poser5, and it turns
out that the vertices at the point of the cone aren't exactly
coincident. What it appears to so is take a cylinder and shrink one end
until it's *almost* a point. It actually uses 4-sided polygons for the
surface. Each polygon has two vertices on the base and two vertices at
the apex of the cone.

-- 
Mike Williams
Gentleman of Leisure

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