And really, regardless of how much faith you place in these stats, this is very reasonable. He was consistently one of the best defensemen on the team, or the very best. Now, he's one of the very worst on the team. Relative to his teammates, he was always a stud, and now he's horrible.
I think people are overlooking the most simple, rational explanation as to why Vlasic has declined. He's 32 years old, and just played in his 1,000th game. The research on aging curves all suggests that in terms of raw impact, hockey players decline a little earlier than conventional wisdom would suggest. Vlasic's peak was from the ages of 21 through 29, with his best season coming at the age of 26, and then he started a pretty sharp decline in his age 29 season, which turned real bad in his age 31 season. Age 31 is a major inflection point for skaters.
Vlasic might be following a bit more of a pronounced aging curve than most NHL players do, but I think he might just suck now. He also came into the league and played a lot of regular season and playoff games at a very young age, which doesn't help either.