Why is this so often a question? There are actually very few exceptions to this: casts are expected to perform all 8 shows a week. There are a FEW roles that have an official alternate that will regularly pick up one show a week. But just like "regular" jobs, they are more often there then not -- but they get vacation and sick days, too.
And yes, there are some performers with terrible attendance records, but most do their jobs.
If we're not having fun, then why are we doing it?
These are DISCUSSION boards, not mutual admiration boards. Discussion only occurs when we are willing to hear what others are thinking, regardless of whether it is alignment to our own thoughts.