Why is considered a badge of honour to be from 'the North'?

http://djtees.com/tshop/store/listCategoriesAndProducts.asp?idCategory=1893

Manchester in particular is what I dislike. The number of people you meet who come out with "I'm a Manchester lad, me. Well, Rossendale. Its about half an hour's drive." is staggering.

How come its cool to be from Yorkshire but not as cool to be from Hertfordshire or Kent? Why aren't there any "Cornish and Proud" tshirts anywhere?