Loading in Three.js
Polygons: 67340
Vertices: 202020

Loading in 3ds max
Polygons: 67340
Vertices: 36478

So the number of polygons are the same, but the number of vertices is about 5 times higher.

As I mentioned before, there are a number of reasons why vertices can be duplicated - the one I am most familiar with is that the mesh is modelled with quads (4-sided polygons) and these are not supported by three.js so they are subdivided. But that is not happening here as the mesh is already triangulated, and in any case number of polygons is not changed here.

Also, I tried re-exporting as a .FBX and loading this I get the same numbers from three.js as with the .OBJ file.

There are other reasons for multiplying vertices (to do with normals and UVS I think), but I’m not familiar with these.