IIRC during my own research days (when i was looking for my own wheels) this is just the way they are built. In the WORK (very glossy) brochure they explained these types (and the 3 piece ones too) and it seemed to me that it would only make a difference when you went to try and repair broken wheels. Mine are 2 piece, for example, Kev's are either 2 piece or even 3 piece. Someone else want to chime in?
for the sizes, post here too as you have to make sure they fit, don't forget to ask if they clear the Brembos or not (offset related)!