That mirroring thing is really weird. I remember having extended desktops on the G5 iMacs and I assume no meaningful features were droppped (perhaps HD playback on external monitors).

As for software RAID vs. hardware, current processors are usually so much faster than spinning disks that I suppose hardware RAID exists currently only on very high-end systems. As for the low-end systems, they make the processor do a lot of work, so, that more or less evens the playfield.

Macs also have a much longer useful life. I still use a G3 iMac that has been serving me flawlessly since it left the factory.