It isn't as simple as the size of the fan base or what comes through the gates, as it happens. When you just isolate one very small element of Rovers dealings over the last few years with Phil Jones being an example. When you unearth a Gem like him, it can keep a small club very competitive for a long time, if the club strike the right deal. The transfer fee was huge and given that he was' home grown' the profit on this was substantial. It's a real sham that we seemed to waste it.
Granted these sorts of transfers are the exception rather than the norm, but one big deal ever now and then, can eliminate the difference between a club with say 15,000 week in week out and a club with 25,000. This may mean clubs with smaller supporter bases, may invest in youth development a bit more and also be a bit more imaginative with sell on clauses and the like.