A handy person could probably do the brakes. He isn't going to true the wheels properly. It might be straight, but it may have too much tension and cause a failure at the hub later. If the stem is not inserted at the proper height it may break off. Joe garage mechanic doesn't always know these things.
I do my own bike maintenance (except building or truing my $500 rims), so yeah it doesn't take a 4 year degree. But people aren't as handy in general as they once were, and bikes are more complicated.
It's just a view held by many avid bikers such as myself. I'm not declaring any new law be made.
Dang! And to think, I used to work on every part of my bicycle, whether it needed it or not! Either I was an amazingly good 8 year old mechanic, or I was really lucky.
I did know enough to make sure my brakes worked, the seat height wasn't going to change mid-ride, and the wheels weren't about to fall off. These were handy tips I was taught by experience.
If I could figure out how to true rims with straight pull spokes, I'd save myself enough cash every year to take a cruise. That or I need to ditch the XC wheels and just buy a set of Rhyno-Lites and be done with it.