I would agree, but for 1 thing: A frame that is not manufactured correctly *can* shorten the life of a tub.
Bare wood, like bare pine, *might* rot, especially if you have a leak that goes undetected for a significant amount of time. Some metal frames *might* rust based on the kind of metal used and the kind of coating used. Â
Wood frames (and metal frames) must be structurally sound. Â No 1x1 wood holding up the shell and all that water! Â 
There *are* valid structural questions to ask, but *both* can be done right by a *quality* manufacturer.
-Ed
I agree with Ed 1000% This debate is getting silly and out of hand. As Bethstar pointed out other equipment will likely fail long before the frame structure. This debate, like TP v FF, 2-speed v circ, will rage on. Consumers and dealers that purchased one because they were convince the other was better will continue to bash the other.
HTMan