That's how I've learned it around 1995, and that the division between /[s]bin and /usr/[s]bin has the reason that the former are required for system boot, while the latter are mounted via NFS from a central server - why waste local disk space when these would be identical for every system anyway (in a homogenous environment, at least). While that made a lot of sense to me back then, I've become aware that it might not be absolutely accurate, though.