Builder vs Designer

I was talking to Tim about Gravity Group coasters, and the fact some of them are built by TGG (Hades, Voyage, Ravine Flyer II) and some are built by Martin & Vleminckx (Boardwalk Bullet, Fireball).

Do you think it would make a difference in the construction, or is it simply distribution of resources?

Incidentally, I notice M&V's are all-wood, whereas Gravity Group's are wood/steel hybrids.