In the case of Graves, you're dealing with a depth forward who clearly has no impact on the fate of the Senators, since they're currently sitting in 2nd place in the East. As such, I don't have a huge problem with the Sens keeping Graves in the minors. I would feel differently if Graves played for Carolina, in which case he'd be a first-line player. That being said, I wouldn't mind seeing Graves placed on waivers so that he'd be available to other teams that could actually use him.
With Irbe, you're dealing with a backup goaltender who clearly has no impact on the fate of the Flyers, since they're currently sitting in 4th place in the East. I don't have a huge problem with the Flyers keeping Irbe in the minors since he's barely better than Noronen. Again, I wouldn't mind seeing him placed on waivers, either.
In the case of Houlder, you're dealing with a depth defenseman who plays for a team with financial problems. It would be silly to force Colorado to play Houlder just for the sake of driving the team into bankruptcy. Houlder has cleared waivers on more than one occasion. I would feel differently if Houlder was the Avalanche's #3 defenseman, but he's not.
I do, however, have a problem with the Hurricanes benching their leading scorer, especially considering that finances aren't a problem......hint, hint.
Basically what I'm saying is that, if the player is good enough that he should be playing an important role, then he should be playing. It's not fourth-liners I'm worried about here. It's teams not playing their first and second-liners.