No MS>OS in Dungeons?

I just ran Alcatraz with a Bear Tank who had all unwanteds HR'd.
The Caster Trinket from the last boss dropped and the Tank needed on it because he has gear for Bear/Resto and Boomie so apparently its fine to roll on everything that would be an upgrade for any of his offspecs, because in his words "there is no MS>OS in a 5 man dungeon".

What do you guys think of it?