Let's not take the Beatles let's use a different example. The Royal Philharmonic Orchestra, The Sydney Philharmonic, The Halle, The Royal Scottish National Orchestra and so many other Orchestra's around the world. Not to mention Big Bands, Brass Bands, Concert Bands etc etc etc.
Ok, but who was I actually referencing as working musicians? Obviously these guys have to read music - that is the tradition within their field and will always remain that way. But what is the ratio of 'Classical' musicians to more contemporary styles? I would most likely say that those who perform in 'Informal' environments are most likely in the vast majority - at least in the UK - and amongst those the vast majority probably don't read music. With the demise of the Major labels, there are far fewer 'Session' players travelling around into studios. Live there are still Session players - but the ratio of non-Session to Session players probably biases in the favour of the non-Session players - the majority of which might well not read music.
Unless you're saying that people who don't read can't be musicians - which is just pure snobbery.
When did you sit GCSE's? I would have thought that I sat mine far more recently than you did. They are not worth anything academically and therefore become an exercise that is distinctly NOT academic. At least within the Arts courses. Why do so many Musicians come from Art School? Most of Pink Floyd did for instance, and so did Brian Eno (although he is an exception with regards to his theoretical knowledge). A lot of musicians do not actually study music academically anyway and the GCSE really is not treated like an academic exercise. I sat mine four years ago and I doubt little else has changed.
The most academic exams I've ever sat for music were my Classical Singing and Theory exams. The level of knowledge required there was far higher; but they were Formal examinations the GCSE isn't necessarily a Formal qualification. There's nothing formal about the GCSE teaching theory. There isn't much mention of theory - it's much more about listening skills and interaction with others in the musical environment. Unless that's changed drastically in four years - I'd like to see evidence otherwise.