I'm not sure about memory management, but that's just one example that the parent is listing. Another example would be that neither windows or macs had preemptive multitasking for quite a while - windows didn't get it until win95, and I think macs might have had to wait until osx(?) (I'm pretty sure AmigaOS had it all along).
The point is that it's perfectly possible for an OS to be updated to accommodate more modern systems. It's been done before. It's been a while since I played around with AmigaOS 4, but that has most(all?) of the features you'd expect from a modern OS. It'll run on a multicore system with USB ports and nvidia cards and wifi and most(all?) of the modern goodies you'd expect. if it ran on x86 hardware I'd absolutely be looking into using an AmigaOS 4 workstation. Unfortunately the hardware it does run on, while super cool and impressive for an amiga, is too exotic and expensive for my tastes.