I don't think you made a "mistake" at all. For a shop owner to chew out a customer - not just a tire kicker, but someone who actually had bought there and brought in additional customers! - is totally out of line and asking to go out of business.
All excellent points. The walk-out-with-it-today factor (your #1) is a major reason I've bought lots of gear, at all price points, in stores rather than online. If I want to change the strings on my bass I want to do it today, not a week from now when the mail arrives even if that saves me a couple bucks. If my cable broke I want a new one to practice with today. Bigger items like instruments and amps I want to buy the one I tried out rather than one sight-unseen, unless I've got really good reason to have confidence I'll like it and it isn't available in any local stores. Above all, your #3 point is essential - I buy in stores because I LIKE the stores, I LIKE having them in the community, and I like the guys running them. If they're going to be rude or stubborn or not value my business, though, they're sunk. The personal touch is the area where they offer something a website seller can't (and
Sweetwater works pretty hard to imitate it).