I guess because I happen to be on holiday in Central London...
I haven't seen so many Bromptons in all my life...even the cool new S-Types. Second in numbers are Dahons and re-badged Dahon-clones. Third are what appear to be a modern incarnation of the Raleigh Twenty. I also caught glimpse of a Strida or two.
Definitely a much larger folder presence here in London compared to San Francisco.