Eh... sh only refers to the generic specification of a bourne-family shell, usually bash or dash; almost nobody is actually using the original Bourne shell.
sh refers to a POSIX shell. The bourne shell (bsh) is not entirely compatible with the Bourne Against Shell (bash), and bash will switch to a compatibility mode if called as sh.
Additionally, many distros, including Ubuntu and Debian, do not use bash as their default shell. (Ubuntu/Debian use dash, Arch uses zsh, Alpine uses busybox sh)
1. Except on Android, stock Debian/Ubuntu/etc., and in the bootloader and initramfs of my embedded OS;
2. I'm guessing you actually meant 'Bourne Again Shell' instead of 'Bourne Shell'.