By 4" in the back, I'm talking about suspension travel. This is riding, not State Prison.
Anyway, the sort of riding we do varies. There are a lot of smooth gravel roads, where short-travel works fine, but there's also sections where it gets very rough and rocky, and some where there's whoops, and some that's just plain chowdered from trucks driving around in the winter slime. The best combination for it all is a relatively soft set-up with long travel (basically anything 1977 and newer) so that it can absorb the bumps and such. A stiff suspension set up for modern motocross-type jumps would be a bit harsh for this kind of riding, so it's convenient that older bikes were made with a bias toward rough terrain rather than jumpy terrain. I hear modern Japanese motocrossers tend to be twitchy, too, which would really suck a lot of the time. Even on a Husky, which has forks set up like Peter Fonda's Harley, can feel a little unstable in a rut. Of course that's where the... uh... "M---o Magic" comes in.