Even Dahon still stiff's the US. They really should be offering both 7 speed and 3 speed Curl's, but after the 3 speed only, it is a bit of a non event. I'd buy a 3-6 speed Brompton, before I bought a 3 speed Curl, unless it was a fab deal used.
Add SF to your NYC & Portland comments. Calling 80% Urban, does that mean they're counting suburban sprawl? Transit, density, car unfriendly (traffic and cost of parking) and actual bike and increasing bike infrastructure make a big difference in those cities.
I do find the discovery of multi modal and government incentive SoCal commuters on this board, interesting. Definitely not aware of them as a kid, though I was thoroughly aware transit sucked. I did borrow my first bike and own two bikes, as a kid/college student. I was a weird & poor Southern Californian, now that I think about it. I didn't worry about not having a car, because everyone else had one, so getting a ride wasn't really a problem. I got my license way later. I've still never owned a car.
I'm sure things like Warm Planet's bike previous Caltrain location, helped expose people to folding bikes in SF, which makes them more frequent in the city. I imagine as density and traffic and parking costs increased, biking\walking culture increased. I mostly see Dahon's, Bike Friday, Downtube & Bromptons, though. Which is interesting, because I know there are Terns and I know people are buying them, but I haven't really seen them in the wild. I certainly haven't seen anyone else with a Mezzo. I definitely didn't have the opportunity to buy the Mezzo/Ori or Frog, I really wanted.
Oh well, I got the Mezzo i-4, now. So next folder is mtb foldy (20" or under) or a present (possibly a bmx, not a folder) for Miss I'm never gonna buy a bike, because I'd always spend more than $100 on something else and nothing under $100 is 20 pounds or less and actually functioning/comfort/offroad/space saving. Much more likely to buy mtb folder, than attempt to gift impossible to please.