downshifting without matching revs also contributes to gear synchronizer wear. And if you force it, not only will the driveline be subjected to shock, but you will also upset the car's balance because of the sudden engine-braking.
once you have downshifted and are engine-braking, you are also wearing off the opposite faces of your gear teeth, especially the rear axle hypoid gear. Of course these could be negligible, but contribute to additional wear nonetheless.
but when i downshift from 5th to 4th to 3rd on an offramp (with proper rev-matching of course), i tend to forget that because of the glorious sound that inline6 makes when engine-braking in 3rd at about 4000rpm.
rev-matching is especially needed for the benz because of the wide spacing between ratios, and the high rotational mass of the engine/flywheel.