When you start ordering clothes online you discover in a real hurry that sizing is agonizingly approximate on the best of days. The same size can be significantly differently sized between batches. I figure it's due to fabric being tricky to work with in a factory setting. One worker might sew the seam allowances a smidge tighter than another which can easily add up in a garment.
That said, there's nothing quite like knowing exactly which size of which model of which brand shoe to buy without having to go shopping. It has changed buying shoes from a weekend-long hunt to a 10-minute online order which gets me exactly the same shoes as the old pair. I've been looking for a good brand of socks to do the same trick with, If I can just find a single model of nice wool socks I can order online I'll be so happy -- cold feet and ill-fitting socks are no fun.
Ironically, I've heard complaints from people who've re-ordered things this way that the fit changed between orders.
> I’m sure that in another ten years I’ll just give Amazon my measurements and tailored clothing will magically appear whenever I order it.
Other sites do this. I'll be a bit sad if Amazon crushes this market too.