It's more a prestige feature more than anything else. Same reason why Saturn cars with plastic doors didn't catch on. When you're buying a camera in the $1k+ range, it better be made out of premium materials. Plastics are considered cheap, even if the plastic strength matches metal strength. Anyhow, just another reason for Canon marketing to give us less for more in the name of product differentiation. Nikon at least kept the mag. body on the D7000.