Heidi - you've touched a raw nerve I think. The answer to your question is probably "nobody but Neil and those who've worked with him really know for sure". As for whatever is better - to read/write music or not - thats all personal and subjective.
Like some of the others here I can read and write music but I never do when I write songs. I agree with Heidi, at least in my case I feel the more mathematical it gets the more magic gets taken away. John Lennon and Paul McCartney could never read or write music and they didn't do too bad, did they?