Number of ingredients for su****: precision needed

I recently heard that you must not make su**** with four ingredients,
as four is the "****" symbol (meaning death). Obviously, that statement
made in the media was incomplete. So here I come for precisions.

- Is this a rule or just a rare superstition ?
- Does it only apply to maki, or also to other pieces ?
- Does the rice and the algae count as ingredients ?

Thank you for enlightening me,
Max