Checking lines really don't exist much anymore with how deep teams are getting. Pretty soon teams are going to need 4 lines of guys who can chip in offensively because that's just where the league has been heading with some of the 3rd lines that teams are employing now.
"Shutdown line" is such a stupid term. I guarantee most good top 6 lines in this league could be employed against the other team's best and shut them down. I guarantee Crosby could be a shutdown center. The big line in Anaheim is a shutdown line. Boston could shut down anyone with a couple lines that they have. Toews' line in Chicago is a line that is relied upon defensively to go head to head, as was Richards in Philly. Who does Detroit employ in defensive situations? Both Datsyuk and Zetterberg. What about Vancouver? I believe that honor goes to Kesler who is a top 6'er. Defensive responsibilities depend on the players...not the line, as I have just shown.
You don't have to have a big defensive center as your 3rd line center, especially if someone in your top 6 is really taking the brunt of matchups. What you would then want from your 3rd line is scoring depth, which the Pens have guys to do just that.