I came across a page on your style guide today via a Washington Post columnist who called you out on it. It carries the following text:
The overriding principle is to treat people with respect. That usually means giving them the title they themselves adopt. But some titles are ugly (Ms), some misleading (all Italian graduates are Dr), and some tiresomely long (Mr Dr Dr Federal Sanitary-Inspector Schmidt). Do not therefore indulge people’s self-importance unless it would seem insulting not to.
So, your style guide in 2014 says “Ms” is ugly; and as for the preceding “but” and the last sentence, it is not clear what the intended message is, but it strongly suggests that women who use “Ms” are seeking indulgence of their self-importance and need not be thus indulged.
I know that you use Ms. very often in your own publication, as does everyone else. These days Mrs. is getting rarer and Miss is almost unheard of; in the case of Angela Merkel, for instance, you sometimes seem to use “Ms” and sometimes “Mrs”, which, at the very least, is inconsistent.
There is also the basic question of accuracy: originally “Mrs” meant “wife of” and was generally followed by the husband’s full name (“Mrs Dennis Thatcher”); these days “Mrs Margaret Thatcher” is acceptable, but what about women who have chosen not to take their husbands’ names? “Mrs Steffi Graf” sounds simply wrong and, yes, ugly (as does “Mrs Merkel” for that matter, since her current husband is not Mr Merkel), and “Miss Steffi Graf” is both wrong and condescending. Indeed, this is the factor that caused the late New York Times columnist, William Safire, to change his mind and endorse “Ms” back in 1984, though it broke his heart to do so.
It is 30 years since Safire was converted, and about 40 years since the “Ms” abbreviation became widespread; perhaps it is now time to update your style guide?