Lieby is one of the top catchers in most offensive categories. Another two backstops are having good years, Jason Kendall and Dave Nilssan, and they could be the only players from their teams added to the squad. There's a similar story in the outfield. Bobby Abreu is one of the best hitters in the league at any position, but he's overshadowed by long-time stars like Larry Walker, Sammy Sosa, and Tony Gwynn. Other guys are having good years, but most of them haven't done as well over the past two years as Abreu.
Third base is a little less clear.
Scott Rolen has been recognized as one of the best third-basemen in the game. If he was having as good a year as he had last year, he'd have a better shot at making it. But he's been in a funk lately. The addition of Robin Ventura to the NL has expanded the number of productive third baseman fans have to pick from. So Scott could also be getting a few days off in the middle of the season.