> In those contexts the distinction between bin and sbin is indeed superfluous.
It's not just in single-user systems where the bin/sbin split makes no sense. A lot of sbin programs provide useful functionality to non-root users. My favorite example: On Debian it's /sbin/ifconfig, but as a normal user I like to run ifconfig to see IP, tx information and so on. Why must I type the full path? (Yes, sure, I could use 'ip addr' for that. I am a creature of habit.)
> However, in many other installations the roles of end-users and administrator are fundamentally different and will also be impersonated by different people.
In all cases that I know of tools which you need to be root to be useful also safely refuse to run if executed by a non-root user, so there seems little *need* to segregate them.
> In those cases, the distinction between bin and sbin limits "namespace pollution" of tab-completion for normal users, i. e. tab completion will not suggest executables which cannot be executed by non-privileged users anyway.
There are so many binaries in /usr/bin these days that I don't think a few more will make much difference. "Cleaner tab completion for some users" seems like such a tiny gain.