Emacs is a bit crazy about it... it has its own set of input modes which include modes you may not be familiar with. You can use various IMEs that plug directly into Emacs rather than relying on a systemwide IME (which was neat back when systemwide IMEs didn't work well), and there are systems like RFC 1345 (type &e' for é, &e* for ε, &12 for ½, etc), or TeX (type \'e for é, \varepsilon for ε, \frac12 for ½, etc).
So many people have their own preferences for how to type these characters, write an input method for Emacs, and get it included.
So many people have their own preferences for how to type these characters, write an input method for Emacs, and get it included.