the comments i remember from various interviews is it was originally just about weight, due to lighter wood being harder to find vs his specs for bass weights (as already mentioned)... this is why the chambers are like slots instead of larger pockets, to actually avoid any sort of acoustic behavior from larger spaces (the opposite of Mike Tobias' goals, BTW).
HOWEVER, he does comment that it did end up affecting tone maybe a bit more than originally anticipated, but not in a bad way. It's just yet another personal preference thing at this point, though chambering is still (obviously) done by default nowadays, and solid is generally by request now (for NYC).
