Or maybe author's native language is not English. :D UTF-8 does require twice as much bytes for Cyrillic, for example.

Besides, there's a lot of other operations that happen in modern OS that makes text editing more expensive. E.g. modern applications need to account for bidirectional text, so things like "determining the correspondence between a character on screen and in memory" suddenly require table lookups to determine if the character is RTL or LTR.