I understand the question, as well as the idea that it has to be a convention is a bit loopy. But, rather than bash those who expect 72, I'd like some analysis of how it got to be that way.
Lets go back to Tony's original question, and ask just how many "classic courses" had par of other than 72? Is it 5%? 10%? 50%? I really don't know, and if anyone has done that math, I'll bet they would be hanging around here!
My guess is that courses had got to that convention even before the Golden Age.
Then let's ask why there is a fascination with 72. I made some guesses in my first post, and will add that to many, the idea of a par at "even fours" was appealing. Why, I don't know, but announcers would rather say that than, "He's one under 3.9's" for the day.
If the golfing public back then was similar to how it is now, then handicaps and oher things, and didn't give enough of a hoot about someones idea of the best 18 golf holes, as long as they are good ones.
For that matter, for Tony and others, if you play 18 enjoyable holes, how would you know that there may be a theoreticlly better 18 by changing a par? Or what holes were foregone because of a par rotation, and which were foregone because of other things, like not fitting the overall scheme?
In any event, does anyone have a theory on what influential course, golfer or architect brought us to 72 as standard par?
Forrest made my point about current balance better than I. I will add that some wonder if someone like my 15 year old son, who plays nine holes every day after school would have the same handicap if he played the front nine at a par 34 far more than a back nine at par 37, so that was my point on handicaps. Don't know how it would really be affected, even though our course is a 35-36-71.