If you think this city should be in the top 5 or something then you are under estimating how long it takes to build a fan base.
Which is why I'm glad we're celebrating the 10th anniversary/completion of 10 years, because it reminds people of that. Nats are consistently ranked above solid teams like the Braves, Reds, Pirates, and A's (especially) in attendance on a yearly basis. Then you have teams like the Rockies and Cubs which always rank above average. This season the difference between Texas, ranked 9th, and the Nats is an average of just 1,720 per game. Other factors like ticket prices and promotions play a part also.
So yeah, it will be a while before the Nats rank up there with franchises like the Dodgers, Cardinals, Yankees, Giants, and Angels (top five for 2014).