Oh you mean Dawn French being a quite believable Rosie Bales,
and then of course there's Pauline Mclynn being Mrs Doyle from Father Ted
Sue Johnson, Mum from the Royal Family, etc.

Perhaps actors get a bit typecast because they have perfected the character and the audience like to recognize that character. The casting director will choose the actor who portrays their vision of performance required, and for me the cast works in "Jam and J".
Just stop moaning and enjoy the show, it's only telly!
Oh and sit back and wait for the CD of the soundtrack. Kate is already getting airplay for the title track.

Andy