Not necessarily, every NFL team for example, their expectations are to make the playoffs and win the super bowl...how you get there doesnt matter. Its the end result.
EDIT: Maybe its different because of the promotion and relegation system, where you can take marginal success (being mid table) as a success in itself.
If you showed up on a Raiders, Bills, Jaguars, Browns, Texans, etc message board and said that you expected the team to win the Super Bowl and otherwise the season was a waste I'm pretty sure you'd be laughed off the board. Most Americans have the critical thinking ability to understand that reasonable expectations are connected to a massive series of factors rather than just IF WE DONT WIN EVERYTHING, SHUT IT DOWN.
It would be absurd to expect Spurs to win the league. What's the point of it even? Just to tell yourself you're striving for the best? If you're not realistic about expectations all you're doing is just lying to yourself. That doesn't really serve a purpose IMO.