This design decision can in practice create trouble with "mis"configured domains where www.example.com is in fact not the same as example.com. This is especially popular in traditional university domains where "university.xyz" does not resolve to a host but only "{www,mail,ftp,...}.university.xyz" does.

Looks like other people agree. https://news.ycombinator.com/item?id=17927972

Maybe useful for you, but really not needed for 99% of users.

ergh