My 2 cents worth
As someone who frequently flies a spam can around the northeast I think I can comment about this.
US aviation works very well. I have frequently being given Bravo transits in the NYC airspace. One day they were holding commercial departures out of LGA from climbing me as I passed over at 5500 feet. Kids thought that was cool.
Outside the Bravo with flight following I've regularly had 121 traffic pass 500 ft above me. The key is they always will notify the other traffic and add something like "I'm talking with him". If they are not talking with you they will steer traffic away from you several miles out. I've seen it happen. I guess that is why they like to get you on flight following.
In this incident the GA plane was inside the Bravo and you can assume the controllers were talking with him or they would have held traffic on the ground.
I do think the controller should have given the UA a heads up with the clearance. The UA crew probably wishes they hadn't made a fuss but they got surprised and no one likes that.
Reading what I do about GA pilots in Europe and other places I realize what a great deal we have. One thing I think makes a huge difference is we have a readily accessible IFR rating that a lot of GA guys have. As pointed out the controllers can tell who they are talking to and the squeaked voice does not get the transit. Cruel but fair.
Other countries could do well looking at how the US does it and consider if their restrictive attitudes are not part of the problem.
20driver