Being in a band, especially on tour, is a job, and some nights you show up because you have to. You see a band enough times, and you can usually tell the difference. Rush was a band that you could tell pretty easily if they were into it that night or not.
I don't need DT to run around. never have. But I want to know that they are at least into it. I've seen shows where they were, and I've seen shows where they weren't. It's something that is not evident in the playing, listening back to the boots, but being there, it's clear.