unfortunatly i've lost track of the conversation, as i thought the original reply, the 'quintessentially urban' blog was to beth not becky. so you can find my reply on beth's blog (in 'comments') on parkour.
in short my argument was that parkour is more than just a physical activity, i.e its urban street culture.

The debate about rural and urban activities reminds me of a weekend I spent in 1988 helping out on a training course called 'Country Wings' for people working with problem teenagers. I was working in deepest Derbyshire, but for this course we headed into Sheffield, and did 'outward bound' type activities in the city. The idea was that the activities would become familiar to the young people, then they would get to practice them in the 'wild'. So we paddled across the rather smelly River Don to a small island and set up a tarpaulin bivouac where we spent the night listening to the sounds of factories. Next morning we cooked breakfast, paddled back, and did things like blindfold rope trails around derelict buildings, using old railway engines for 'bouldering' etc. Brill. And Sheffield climbers have long since practiced on concrete walls and bridges (see a short film from same year called 'Stone Monkey'). The urban and rural are not easily separable.