Yeah the first several Acts have a lot of user submitted things (especially early Act 1, which apparently was a big contributor to a lot of people not liking early Act 1, because people tried to treat it too much like Problem Sleuth), but as the fanbase grew people just started submitting like every possible thing so he just stopped.
Also there was less and less stuff he could do with user subscriptions anyway as the plot got more involved.
--
http://img149.imageshack.us/img149/2664/7b7aaa038007832d461b28c.jpg