I'm thinking about the recent time my T was so late for his appointment with me that I couldn't wait for him and had to leave. (His lateness was due to a brain snafu and poor planning.) He did compensate me for this missed session by not making me pay for the next one. That was a great and unexpected gesture. It felt right and respectful that he did this. I accepted the "free" session. However, if he had called me the morning of the session and told me he was very ill and had to cancel, I would not expect him to compensate me next time. It seems different to me. If he offered, I would decline. In the first case, I took time out of my day and traveled to his office and waited a long time. In the "sick" example, I would have learned soon enough not to go to his office. Maybe that is the difference. Also, having compassion for someone who is feeling poorly.

Don't know if that's relevant to the situations in which a T "excuses" an absence, but it's how I would feel toward someone who is ill vs. someone who just decided not to go that day or was careless and didn't plan adequately.