But trash pulls, when done properly, can well serve the same purpose as the DPS and healing checks we get on bosses right now, case in point: Faust on Savage, while not trash, serves this purpose as well. Trash can also be set up in ways that require group strategies you will needed on boss mechanics, i.e. splitting groups between tanks, making sure tanks are grabbing the proper sets of adds, making sure that DPS is prioritizing kills properly.
The way it is seen now is that trash mobs are just that, throw away encounters just there to slow you down a little, that you rush in and zerg so you can move on to the interesting parts of the dungeon.