I doubt the cabinet is really inert, regardless of bracing. When I had th 202, a pair of LSis outweighed it by 5 lbs. The LSis have some solid cabinets, and they are better built than any of their subs from the 505 down. Weight IS a factor because it means the wood is very thin, and on the 202 it certainly was (knock test). I'm not saying the 505 is like the 202, but I know from hearing the 404 and 505 in the store that they aren't worth their MSRP price. I agree, it is most likely the driver that is the problem, then the amp. I'm not saying it's garbage either, but it isn't worth the price of admission. It would probably be OK if they were charging what bigbassdave's discount price is...but I still wouldn't buy it when there are HSUs, SVSs, Outlaws, etc... to be had.
When I build my sub, the enclosure had only one brace in the center. It weighed about 50lbs with no drivers in it.