I don't think this is true. I've certainly been in a bunch of hairy situations over the years where I had nothing fancier than ed available to me because I was

I don't think this is true. I've certainly been in a bunch of hairy situations over the years where I had nothing fancier than ed available to me because I was in some sort of recovery mode. The single user mode that FreeBSD comes with is lacking vi if, for example, you don't have / mounted yet. Thankfully ed is in the ramdisk.