Quote - Take a quad based mesh that is 600 polys and all quads.

This model has 2400 define vertices.

Now trianglulate the model. Now it has 1200 tris and 3600 vertices.

You just added 1200 vertices to the list in the file, which increases the file size dramatically. Keep in mind that the UV part of it increases in size as well, so does the normals section if it has to be in the file.

I am confused here...  A quad has four vertices.  If I split it into tris, doesn't it still only have four vertices?

I thought that was the point of tri-strips, to build each triangle by adding one vertex to an existing triangle...