I think many people end up turning their sub up and down depending upon the material and source...I know I do! There are some differences with the level of the sub channel from some SACDs or players I've heard. I don't fully understand it but find I'm adjusting all the time anyway!
I think it's still helpful to try to determine a standard. If the levels are all set on my electronics, I can "learn" over time to raise and lower by certain amounts with different sources.
Aw, hell. The guy's right! What are we bothering with this for anyway???