Interesting to read that some people have noticed this even back in the day. Maybe it depends on Stevie's constantly changing mood that it sometimes seems she's just going through the motions.
I was too far away to notice it on Thursday, but I wouldn't blame her if she's tired of the routine. I would only blame them for charging so much money for concert tickets in this case.
By the way, I always think she looks bored and tired on the "The Dance" dvd as well.