Gee, thanks for a link to a search. If I had wanted to look at a bunch of stuff, I would have done that myself. I thought you were linking to a specific article that would explain how you cut metal without leaving a sharp edge. I did check a bunch of articles, but I didn't find an explanation for how you cut thin metal without leaving a sharp edge.
And yes, the top cutting can openers do leave a sharp edge on the inside,, near the top edge of the can. I learned to be careful of that and keep my fingers out of the can a long time ago. The other top seems like an invitation to accidentally brush your hand on the sharp edge.