SA is a small market team, of course they have a relatively small fan base compared to cities several times their size. So what? I don't know how any rational person would say that the Spurs' style of basketball is "boring" this year either. They play a beautiful game, score a ton of points, and have one of the most exciting players to watch in the NBA with Manu (not even counting 2 other future HoF'ers in Duncan and Parker).
What you left out though is that in SA and South, it is all about the Spurs. Part of the reason no other sports team has come there is it is a town that is so dedicated to that team and the Spurs are a victim of their own success. People in SA have grown up watching the Spurs be successful consistently, have some of the greatest players of all time, and have an organization and players that are so integrated with the community. For me I grew up watching George Gervin and being in awe of what he could do, one of my most prized possessions is my signed "Ice Man" poster. Then followed the Robinson era and of course now Duncan. The Spurs are a great example of an organization that has had incredible success against all the odds, they are the only ABA team that has truly put itself in the elite of the storied NBA franchises. Are they the greatest or best? No, but they have an awful lot to be proud of and have done several things no one else has in terms of sustained excellence.
All the other Texas franchises have to share. The Mavs fans are also Ranger/Cowboys fans. The Rockets fans are also Texans/Astros fans. Not many of them would list the bball teams as their favorite either. Not so for many Spurs fans, they are the only show in town in SA and the city lives for them. It is the greatest single source of pride for San Antonio, they are deeply ingrained as a part of the culture in the same way the Packers are with Green Bay. The fact they have always succeeded with less makes the bond stronger.
All of the haters of the Spurs are the worst kind of jealous. The Spurs' organization is about as well run and classy from top to bottom as you could ever hope for a pro franchise to be. They have always won quietly and without any help, they just win. Eventually they will falter if for no other reason than Pop and RC can't continue on forever and it never lasts in perpetuity but the accomplishments are amazing. People don't hate Green Bay for being a small market team that succeeds. People don't hate the Tampa Bay Rays either. I don't get the hate for the Spurs.