The spools on the new BWS highboys we got are rated at 5,000 lbs. just like the pockets. I had them built out of heavy wall pipe and the rub rail they're welded to is 3 inches high and 3/8" thick.
I think it's all BS to be honest with you. Hooking on top of the stake pocket ensures that if your chain comes loose it still won't come unhooked. Yes, yes, I know that every Supertrucker, DOT man and safety guru will tell you that a chain should never be loose but lets get real.