The common misbelief is that the surface on the back of Canon cameras is an LCD surface as it is with Nikon cameras. That is incorrect. Canon build into the camera an LCD screen protector that is easily and cheaply replaced.
I was not aware of this, and that's interesting to know. What I *was* aware of is that of the 5 Canon DSLR's I have owned in the last 7 years, including a 40D and 5D that I used LITERALLY to death (two worn out shutters and nearly a quarter million exposures total for each), none of these cameras has ever had ANY visible marks on the LCD glass. This despite hundreds of miles of walking with the camera bouncing at the end of the neck straps against shirt buttons, zippers, metal doo-dads on credential holders and knock after knock against door jambs, door handles, counter tops, rocks and trees and thorns and other hazards of nature and sports competition, not to mention the occasional butterfinger drops onto hard floors or pavement. . .
To go a little further to stand this question on it's head, who can report marks or damage to their LCD that would have been prevented by a peel-and-stick screen protector? I'm not saying they are totally useless as there is no doubt there are threats out there I simply haven't run into, but it does seem to me these items have much greater utility as an upsell for dealers than as actual protection for the camera.