then surely it is 'fair' for that person to have paid 70 years full dues?

I will answer your last point from an economist's point of view.
In better economic times, the gap between inflation and COD rates widens. Thus, believe it or not, the clubs position would worsen and they would have to look to increase that factor (or hike up annual dues more frequently).
The clubs current financial position has not arisen because of the current recession, it arose during the stronger economic climate.
During a stronger time, it is expected people have more disposable income and can pay more.

However there is one major factor which is difficult to judge at the moment. At what point do we become 'paperless' and the magazine is only available on-line. Have to face reality, it is likely that within 10 to 15 years the civilised world will be paperless period.
When the magazine is substantially on-line then the whole dues position can be re-visited in my opinion, but until then basic rules of economics dictate that the best position the club could take would be to suspend life membership altogether until annual dues have 'caught up'.