Handling .obj files: Why is it possible to have more vertextextures (vt) than vertices (v)?

The number of position, normal and texture coordinates may be different because two vertices may share a coordinate in one space but differ in another.

Think of a box (8 verts) using 6 different rectangular shapes (one per face) in texture space -> that's 6*4=24 texture coordinates.

Edit: A common uv-map for a box looks like below (14 texture coordinates). I've annotated three different vertices: A, B and C. Note that in a box every vertex is adjacent to three faces which has to be true in the uv-map also. C gets a texture coordinate which is adjacent to three faces, but B has to be duplicated and A tripled to do so.