Actually Pete,
it's not the tip that gets rounded with a leather strop, it's the corners of the blade. Since the leather gives way to the pressure from your finger, you actually make the leather cup around the blade and it begins to form a "U" shape around the blade and rounds the corners off.
EMSNUT, I would strop the ceramic on card as well just to keep myself in the habit. I use Cresent illustration board, kind of like a buisness card, but I can cut longer strips. I don't know if leather has the same effect on the ceramic or not, but better safe than sorry. I had to regrind all my steel blades because they had been rounded, Until Peter Main hipped me to this, I was clueless as to why my blades wouldn't remain sharp and cut with ease. (Now I know).
Marlon