As has been pointed out, Wrigley now has a higher capacity than US Cellular. It's bigger now, but up until the last year or so that wasn't the case and the Cubs outdrew the Sox nearly every year since the the Trib has owned the team. Fairweather fans are one thing, that number will fluctuate depending on who is doing well but I don't think there's any doubt that the Cubs have a bigger "diehard" fan base in Chicago than the Sox can ever hope to have. As someone else pointed out, other than '83, the Cubs have pretty much owned Chicago since 1969. So much so that Veeck almost sold the Sox to an out-of-town buyer and Reinsdorf had to threaten to move to Tampa in order to get the city to build that abortion they play in now.