But hasn't the modern equipment, specifically the design characteristics of the ball, allowed the ball to curve less?
At least that is one of the cries of Mr. Nicklaus himself, that the modern ball (and modern golfer for that matter) can't be worked. Since the amateur golfer is using the same ball, it should mean the same at that level.
However, what I do think has increased lost balls is the modern golf course. Poor pieces of land which dictate forced carries over ravines or water hazards and housing development courses that have narrowed holes come to mind as primary evidence.
If more courses were wide open like TOC, the quantity of lost balls would decrease.