Oh I'm fully aware there are a thousand different ways to accomplish similar results. Further to your point, you can also support multiple physical users without actually running a multi-user system as well (eg Windows 95).
However you have to bare in mind that this tangent did start off as an exercise in generalisations so I was following on from that by pointing out that many current multi-user systems also use user accounts as a tool for reducing the exposure a process has. While you'd obviously agree that it's a long way from being the most secure method of hardening a OS, it is still a pretty typical way for many desktop systems to operate.
However you have to bare in mind that this tangent did start off as an exercise in generalisations so I was following on from that by pointing out that many current multi-user systems also use user accounts as a tool for reducing the exposure a process has. While you'd obviously agree that it's a long way from being the most secure method of hardening a OS, it is still a pretty typical way for many desktop systems to operate.