I agree with you, but redundant storage is not the same as a secondary image for an OS.
I haven't seen many issues with the processor or nic dying outside of a lightning strike.
Power supply and harddrive failure I have seen, so that's a great addition.
The one I have seen more is corruption and these redundancies don't solve that, nor if the primary goes completely down. Those would be the next step. If the OS breaks, then I doubt it magically loads the good one from the other half of the RAID 1 because both sides would have been updated with the bad data.