I think merchandise sales are a terrible indicator of a fanbase's devotion, unless you somehow control for the advantage of having top superstars on the team. LA's going to represent well based on attendance and the volume of kobe jerseys sold, but it's hard to extrapolate that into the most passionate fanbase. My disdain for the Lakers aside, I do think they have a fairly passionate fanbase, but I find it hard to believe they outweigh places like Indianapolis, Portland, even New York.
And as far as Boston goes, until the KG trade, getting an average Boston sports fan to talk Celtics was near to impossible. When the Celtics aren't contenders, they don't command as much attention as the Sox and the Pats IMO. It drove me nuts, as a basketball junkie. I have a hard time categorizing Boston as a basketball-town, even though we Celtics fans are clearly top notch.