You probably have to take into account that U2 has been gigging since the late 70's, and during the early years more often then not it was the house engineers who shoved their mics in front of the amp, not U2. So Edge is probably very much used to and comfortable with Shure mics as that is what you will get 99% of the time if you're gigging.
Also you'd be surprised how many guitarists who are utterly anal about every aspect of their guitar tone, from the strings and screws on their guitar, to the cables and pedals into their boutique amps, are utterly clueless to how their awesome setup gets miked up at a gig. More often then not a SM58. SM57 if lucky. It's like their thought process stops at the amp and they think 'my shit sounds awesome, job done'. The total process includes miking the amp with the right mics and knowing where your preferred sweet spot is. Then do what the pros do, mark that sweet spot with duct tape and list your preferred guitar mic(s) in the technical rider. And if its something really exotic, supply it yourself. If you ever get the chance to do an A/B test with different mics in a live venue, grab it!