It has the buttresses but you can have the vault without those becouse they are two different objects. The external edge of the vault can be streched whit a modificator (like FFD2x2x2 in 3dstudioMax). I use this vault for an ambientation, a castle, for a UDK game.
I give the files as: 3dstudioMax2013 default scanline 3dstudioMax2013 vray Fbx Blend Obj 3ds DXF2000 the voult is just unwrapped and I give the textures: diffuse, specular, normal
good fun.