You're right - I should have that some people seem to think that and that there are a lot of gray areas in between.
Personally I'm probably a bit extreme on the "DM is always right" side of the spectrum.
The DM may always be right - but that doesn't stop or excuse the DM from being a jerk!
I try to keep that in mind when ruling "Is my rule really what's best for the game, or am I just being expedient for myself?"
I don't always get it right - but I try not to be a jerk when possible.