If using "tape" in our gear really is normal I think it's one practice that should be stopped. So what if it's cost effective. Companies should be able to develop a nearly as cheap solution or material BESIDES using "tape". Be it camera manufacturers, hi-end HiFi, automobiles..etc. If you're okay with the knowledge that some kind of "tape" has been used in your gear fine. I'm sure it would bother most people.
As a temporary measure...if it solves a problem when you're in the field...sure. But for companies to do this??
Any how the light leak issue really isn't an issue in the end. At least Canon has addressed it with some kind of tape and possibly offering future models with some kind of mechanical fix (as some one suggested).