The latter is my theory about music notation; that inertia is not even at issue yet because there are no serious alternatives.
And inertia might never be an issue, because music notation is a fluidly changing system. TCP and qwerty/Dvorak are static systems that don't ever change, so you can argue about which one's better. Music notation is changing and improving, so it's hard to suggest that people are resisting change, and hard to suggest that something better will supplant it, right?
I agree with your theory in general though, outside of the issue of music notation, and I think a lot of people do. It's just a matter of finding the right examples that clearly demonstrate it. And it would be really interesting to somehow quantify the amount that something needs to be better before people will adopt it. It's like static friction in physics -- it takes more force to get something started moving than it does to keep it moving.