Those calculations ignore two things:
The club shaft and left arm are almost never straight. The distance from the left shoulder to the clubhead is rarely 67", and is only 67" for a fleeting moment in a golf swing.
The club accelerates, it isn't traveling the arc of that thing at a constant speed. It's accelerating from 0 MPH.
My husband said the same - that nobody had ever commented on his swings or offered advice but he noticed me getting them almost everytime we are at the range. Strange.
People do really walk up to give swing tips! It is creepy because you don’t know how long they have been watching! I get the most unsolicited advice at Sandia. At Tanoan, people like to socialize and someone will always stop by to chat or talk about swings. I have had a few people giving me tips at Arroyo, and some asking for tips which I suggested they ask a pro at the shop. Paako is the only place I find peace and solitude because it is always empty...