when properly motivated, a Texan can pronounce 'ranch', 'wrench' and 'rinse' almost the same...sort of 'rainch'. And I used to listen in horrer as some kids I knew discussed their grandfather plowing his 'filled'.

I sincerly believe some people cultivate (some subconciously, some not) these variations in order to 'announce' their cultural identity. Senator Howell Heflin used to wield his accent like a club in committee meetings. He knew very well what the reactions to his extreme drawl were, and relished them! I suspect that many speakers of UK English also identify themselves to their peers by their particular dialect/accent.