Certain ball head may have been designed with L-plate use in mind. Therefore, rotating 90• I use case is handled by the L-plate. So the designer may have use this fact to achieve better: smooth and fine, lower by upright only. If I made a ball head, that's how I would approach it.
Salib: why always Canon????
Please elaborate? I would like this for Nikon mount also but reading that wiki page I don't know the reason why not :(