Why can't the English learn to speak?

Robyn has commented on the "English" Language...
In 'My Fair Lady', Colonel Pickering moans: 'Why can't the English learn to speak?' (His friend Henry 'enry 'iggins Higgins also moans: Why can't a woman be more like a man?' but that's another story...).
Pickering claims he can identify a person's origin to within six miles by careful application of the science of phonetics. And I think he's probably right. Certainly, when I went up to university in Sheffield, I met a fellow student who correctly told me which school I went to simply by my accent! I met her again recently, for the first time in 14 years, and she reminded me of this.
I've moved around the UK a bit myself, and I've noticed various vocabulary and idiomatic changes from 'proper' English (i.e. that spoken in Sevenoaks).
In Sheffield, the 'while' means 'until'. e.g. 'I'll wait for you while six O'clock but then I'm going.' or 'Today I have to work nine while five'.
In Bristol, a word which ends in a vowel will usually attract an 'L' at the end. So, when I went to my first Bristolian Deacons' meeting, I was met with: 'Have you got tonight's agendal?', and 'That's the ideal!'
In Bristol, plimsolls are daps.
In various places 'ignorant' means 'rude' not 'unknowledgable'. e.g. 'That driver who cut me up were right ignorant!'
In South Wales, 'now' means 'eventually'. e.g. 'I'll do that for you now' means 'I'll do that for you when I get round to it'.
Which leads me to conclude that I'm more ignorant of English than I thought, and that it'll be some time while I work it out, which I'll go and do now.