Our expectations now, unfortunately, still should be that backspace is for underlining and overstriking. The man system still uses the TTY-37 conventions, for starters. Indeed, groff, which when it was created was made capable of using ECMA-48 control sequences, was in the late 1990s and early 21st century forcibly dumbed back down to TTY-37. FreeBSD recently switched its manual processor from groff to one that has no ECMA-48 capability.
* http://jdebp.eu./Softwares/nosh/italics-in-manuals.html
* http://jdebp.eu./Proposals/ul-manual-page.html