It's convenient there (and probably not accidental!) that Unix usernames are usually lowercase, so if you want to run a command like ~otheruser/bin/cat it won

It's convenient there (and probably not accidental!) that Unix usernames are usually lowercase, so if you want to run a command like ~otheruser/bin/cat it won't conflict with an ssh escape sequence (although you won't see the ~ appear until you've typed ~o). On the other hand, ~Randomuser/bin/cat would be impossible to type immediately at a new command prompt over an ssh connection (though of course it's possible to run such a command by typing anything such as "x<Backspace>" first).