As a Readingipolitan who'd lived in Deeside a few years ago ...
I noticed many of the scousers that used to commute to Deeside for work, would insist on being called 'Evertonian' on account of their team they supported, rather ludicrous.
Funnily enough, call anyone from Deeside, a scouser and they'd get awfully offended. Although they're happy to call anyone within a 50 mile radius of London a cockney on account of their accent.
Though it may be a joke it isn't one you would do for say for instance about 'Thick Paddies' or 'Jamaican Yardies' or 'Ice cream van Wops' . - just get fed up because the people doing it haven't got the balls to make the same kind of jokes about people or places because it might offend.
I agree, the same tired jokes about regional stereotypes does get very dull. I find they're in the same un-creative league as Mother-in-law, Wife gags and any Jim Davidson routine.