Man of Honour
It's because you're/we're a large minority of the self-transporting public. Think I read somewhere that 3% of the UK population has a full bike license. That could be way off though.
It's the same with Classic Mini's. If you're in one and you see another coming the opposite way, it's the law to flash your lights and wave.
I understand that but when it gets to the stage of differentiating between different bikes it becomes ridiculous. I remember one guy at a petrol station telling my about how he gives the finger to every Suzuki he sees because they're made from "pig metal". WTF? He gave a Ducati a full nod but Kawasakis and Hondas got a half nod. It's stupid.