I've never pegged the 3rd line as solely a checking role. Our two kids-and-a-goat line (Thomas-Pahlsson-Chistov) and rookie set of Penner-Getz-Pears has broken me from thinking the 3rd line is strictly a defensive checking line. Granted, the Shutdown line was that checking line (Moen-Pahlsson-Robby Nieds). The third line has always been an amorphous line that's dependent on the team's talent depth.
With our situation, I think our top-9 forwards are interchangeable. We truly don't have a top line, but we have a top line in name. We're just a bunch of 2nd liners for the top-3 lines. We know Getz is the man, but he also isn't the same man as he used to be.
We do have a dedicated 4th line for checking and enforcement. That's a GM Murray thing. Just like Murray likes an offensive and a defensive pairing on the blue line. The known roles makes it easier to their jobs, which is why Gudz was able to revive his game once traded here. I can't speak about other team's 4th line, though.