[DISC] Why quote colon within a quoted value?

["John D. Ramsdell" <ramsdell@linus.mitre.org>]

The following line in the grammar

<string-char> := <simple-char> | <space> | '\"' | '\\' | '\:'

suggests to me one must place a backquote in front of colons that
appear within a quoted value.  This means that

 "aoeu:oeu", ":", and "bbb:" are illegal values and must be written as

 "aoeu\:oeu", "\:", and "bbb\:".

Perhaps the intention was to write:

<string-char> := <simple-char> | <space> | '\"' | '\\' | ':'

If not, what's the point of requiring the extra quoting?

John