These pics come out in the Mail every year. I've been to the National and these girls are very much in the minority - they just dominate the pictures in the press.
York Races attract the same crowd but somehow doesn't make the news to the same extent - perhaps because it's 4 hours rather than 2 for the national press 
Liverpool is quite manky style-wise though - there's a very bling culture, always has been according to my parents. (I grew up nearby, though there's a gaping chasm between the city and rural Cheshire). I blame Colleen McLoughlin and Alex Curran.