It is about pronunciation. Communication is the watchword and if you do not understand the message being communicated to you, even if the person speaks grammatically correct English, then it it is down to among other things, the pronunciation.
Ah well...I live and learn. Looking forward to hearing all those frightfully decent toffs speaking the Queen's English on the jolly old radio from now on, especially the ones from overseas. (Huw Edwards would never let them get a job at the BBC though boyo) and I still cant understand a word of ATC out of Newcastle so all that lot must have failed their exams.