Originally Posted by MKahrl

I concur with most of what chaadster said but differ in that traditional sizing on traditional bikes was not as bad as described. When fitted at a bike shop or by anyone knowledgeable the equal seat and top tube frame dimensions got the majority of riders in the right zone. Adjustments to seatpost height, saddle setback, and moving the stem up and down got them there. Sometimes the stem length needed to be changed and that was a pain.

Keep in mind that bike buyers of the 1950's - 1980's were interested all-purpose 10-speeds with handlebars roughly level with the saddle. With the specialization of road bicycles to racing-style fit (low handlebars) and sloping top tubes it became much trickier to figure out where the critical contact points were. Not helped by buying bikes online without any sort of fitting.