where are you going, pollard?
attendance is definitely not based on the size of the city. i've seen shows in nyc where there were less than 30 people on a weekend. attendance is based on a combination of numerous things, among them:
local draw/lack of local draw
current "hipness" of band
location of venue
comfortability of venue
how well or poorly promoted the show is
price
day of the week
competition
based on the poor attendance we've had at the warehouse and DC9 for many shows, i truly feel that attendance has declined, specifically among shows aimed at an older demographic. people simply don't come out to shows like they used to. pop-punk, emo, and indie-rock shows do well because that demographic tends to have more disposable income/time than those that are into -- this will sound elitist -- more challenging or underground music, like experimental, noise, jazz, psychedelia, stoner rock/doom metal, etc.
i could be wrong, but after booking, working, and attending nearly 300 shows a year for the last few years, this is what i've noticed.