Comparing the Ultimate Warrior to a training video I seen of his from the early 90's, he does look much smaller than he did in his prime. However, I do not believe for a second he did not take steroids after 1991. In his last run back in 1998, he looked as big as he was in his prime as the WWF champion.
I also seen Warrior speaking as if he was very pro-steroids when interviewed on the news last year giving the impression as if he's open to re-use if necessary, especially seeing he is making his huge in-ring return in Spain.
Here is his full training video posted last week http://youtube.com/watch?v=VHJmcPp_fpg
Warrior on steroids playing a part in Chris Benoit's death http://youtube.com/watch?v=hCM-yAi2SWU