If I remember right there were certain very early pentium 3 processor competitors from VIA and other non-intel, non-AMD sources (with much worse performance) that had integrated onboard SVGA video, where the video RAM was shared with the system DRAM. Meaning that depending how you configured the video in the BIOS, you could have something like a 128GB RAM server "minus" 16GB RAM withheld for video, with like 112GB usable by the OS.

But if this guy is talking about a pentium 75 MHz (socket 5 CPU) that's a totally different generation of stuff several generations before that.

Email bouncing during rare downtimes is hardly that big of an issue - if its actually important the sender will retry, possibly with a different contact method. And for short downtimes most likely the sender's MTA will just automatically retry a bit later - email is designed to work with temporary failures.

There isn't some magic reliability that everyone needs which just so happens to fall into "not achievable with a single authoritative name server" and "guaranteed with two servers". I'm not saying you should never have more than one, just that isn't the registry's business to decide what kind of availability guarantees you need for your domain.