The thing is that Daph didn't have a Manc accent either, it was a sort of Bolton, Blackburn, Burnley twang spoken by an Essex girl (Jane Reeves) and not very convincingly.
Yeah, her accent was definitely well north of Manchester
Saying that, it's an American show and I was once accosted by someone in a shop near to John's aunt's house who said something like "Oh my God! Your accent! We just LOVE Eastenders!"
I know - I put a little video on Facebook once, of me and Mick on hollibobs, and one of my American FB friends PM'd me saying I sounded soooooo sophisticated!