"There are more bikes offered for sale in Brooklyn than Manhattan, but only 8.3% of them are fixies versus 9.5% in Manhattan."
This is key. Fixies as fraction of for-sale bike population <> prevalence of fixies on streets.
From a purely anecdotal angle (supported by BikeSnobNyc's recurring photographs of DIY fenders), there's a lot of cheap mountain bikes in Brooklyn. In contrast, a Manhattanite who commutes by chauffeur or all-Dura-Ace, not-for-sale-on-Craigslist Colnago isn't part of the sample.
This is key. Fixies as fraction of for-sale bike population <> prevalence of fixies on streets.
From a purely anecdotal angle (supported by BikeSnobNyc's recurring photographs of DIY fenders), there's a lot of cheap mountain bikes in Brooklyn. In contrast, a Manhattanite who commutes by chauffeur or all-Dura-Ace, not-for-sale-on-Craigslist Colnago isn't part of the sample.