Rolland,
It's likely very little end sealing was done in historic frames, with little ill effect. Today, however, house-frame timbers are subjected to quicker drying times due to modern heating systems and living conditions. Also, timbers from today's smaller, quicker-grown trees contain more juvenile wood which reacts poorly to these conditions, resulting in highly-stressed timbers with more warpage and checking. End-sealing isn't a cure-all, but will have a beneficial effect in slowing drying times and evening out moisture exchange rates between side-grain and end-grain.
Of course, wood species vary greatly in stability and amount of checking. The old-timers were more likely to choose based on that fact, where today we're more likely to consider esthetics, cost and availability.
Leon Buckwalter
