This is an interesting point and there may be some truth in it. However, as a member rather than STH, in my experience just being a member has been enough to guarantee a ticket even this season. This is proven by the fact that all of our matches have, I believe, reached general sale, rather than sold out to members.
Since membership is a no-brainier for any fan attending more than 2 or 3 games, this does also suggest that we might not see that big an increase in attendance next season. Perhaps some STH will drop down to member level next season with the pressure on availability now gone.
I expect us to average around 16-17k unless we are pushing for promotion.