I was not, but have only been an STH since the 2008 playoffs. I think last year a lot of people didn't renew because the team was looking like garbage so they had a lot of extra strips to sell.
I think the Celtics gambled last year, selling the extra strips at the regular STH playoff rate and asking for a 50% down payment. Had they thought the Celtics were going to make it to the finals I think they would have handled things a bit differently (tried to make more money off the strips).
This year the strips were more expensive, and I assume there were fewer of them.