ok I did search a little the web. I think I've an explanation. If you consider the Archive utility, it has preferences and one concern archive format with three choices (in french
- archive compressé : means compressed archive
- archive standard : means standard archive whatever the actual meaning
- archive dans un fichier zip : zipfile archive
default is the first one and is probably not consistent wrt zip classical format.
I'm working on scripts to automate transformations thus won't have time to test my assumption.