There isn't just one English spelling. One can spell color or colour depending on context (British or American). One can spell naive or naïve depending on context (plain/pragmatical or pedantic/posh). One can spell Francois or François depending on context (pragmatical/uneducated or precise). And one can spell Milosevic or Milošević depending on context (pragmatical or precise). The context of an encyclopedia or other reference work is one of precsision. That's why good English reference works such as Britannica and Webster use the diacritics in foreign proper names.