I can see where you're coming from.
When I first got interested in playing music I did actually spend time trying to learn some theory and like I said I picked up the basics of notation but I started to feel it was getting in the way. I'd much rather sit with a guitar and tape recorder and just play without having to stop and work out which notes I'm playing etc.
In terms of my guitar-playing, its not really about whether or not I can read/write music thats the problem - its not knowing enough about scales and their positioning on the fretboard, which is really just laziness on my part.
I guess its all about priorities.
You rarely find a musician who is a great songwriter, singer, and technically excellent on an instrument let alone one who reads and writes music too. Most musicians focus on one strength and simply don't have time to learn it all and it seems to me songwriting has always been Neil's forte.