Most of the stamped resonators have a series of eight narrow ledges, termed lugs, inset around the edge, on which the spider rests, and as a result spiders designed for use with a stamped resonator have slightly shorter legs. Since the strings connect with the resonator through the spider, it is very important to avoid any sharp blows to the strings, to prevent the spider legs from punching a hole or a dent in the rim of the resonator. Even excessively vigorous rhythm chucking is probably unwise. Pre-war instruments have an undeniable mystique for the hardcore bluegrass picker. In the case of old wood-bodied instruments, there may be some justification for this reputation.
Some folks think it's because the wood has been aged so long.
Others say it's because good quality wood has gotten increasingly scarce and modern instruments are being built with inferior materials. Some just say the craftsmanship was better back then. Dobros are different. Because of the close tolerances of the metal parts, an aging dobro is more likely to develop buzzes, rattles, and diminished volume than improved tone. In short, there is no inherent reason why an old dobro should sound any better than a new one.