Remember, post-injury Perk brought back a backup Center, Jeff Green who was still considered a very solid asset, and a first round pick.
Post-injury Perk was packaged with Nate Robinson. So he didn't fetch all of this by himself.
Asik is an above-average center, and a pretty good defensive player, but I don't think I can put him in the top 10 of his position in any way -- there's an embarrassment of talent at the center position in the NBA this season, both in terms of younger (Cousins, Kanter, Vucevic, Drummond, Monroe) and more established (Howard, Gasol, Noah, Chandler, Lopez, Hibbert, Jefferson, Jordan) players.