I hear this a lot too. The population of the metro area is 3.5 million. They should have no problem selling out each and every gopher game, regardless of the supposed plethora of things to do in the area.
The "big city" vs. "small city" argument used to piss me off to no end. It doesn't bother me anymore, different people enjoy different things.
That said, I enjoy 1-2 vikings games a year, and a few Twins games. I attend the same amount of pro games that my friends who live in the cities metro area do. Yeah, I have to drive 5 hours to see em, but my day to day life, in MY OPINION, is so much better here. Things are cheaper, there is a 5-10 minute commute to work, people seem nicer, and I have a real sense of pride in my community. Grand Forks has its own identity. People who live in the suburbs such as Savage, Andover, Blaine, have their own cities technically, their own governments, but they are seen by everyone else simply as "the cities", a neverending network of urban sprawl. I enjoy my stand-alone city here in the "middle of nowhere". The outdoor activities I enjoy don't hurt either!
Again, to each their own.