Hmm ... something I never noticed, but true. Seems to be pretty common on a lot of the old field designs. The worst I have ever seen though is on a 1971 Munro Canadian Edition game board that I have. It only has 11 yard endzones at a time when the endzones in Canadian Football were supposed to be 25 yards deep. But accordng to a 1972 Canadian Football Rule Book, that I have, on fields that are less than regulation: If the natural boundary of the field is less than 25 yards behind the goal-line, such boundary shall be the dead-line.
And since you got my curiosity up, I measured several others. Some of the 500 models have short endzones by about a yard. Even the most recent Tudor game boards, that I have, have longer endzones by a yard or two.
And... for the history "nerds"... um "buffs", like my self (LOL), the only reason we even have endzones today is because of foward passing. Originally, way back when, forward passing beyond the goal line wasn't allowed. The fields were 110 yards long at that time also.