What? Gate staff looks a the boarding pass. It says "MRS". It is a "MR." who wants to board. Realizing this takes what, .5 seconds? If they don't see it, they are in the wrong job.
From an agent's point of view, this is not weird at all! Just board an Amsterdam flight and you would know what I mean - there are loads of "MRS" who need a shave and loads of "MR"'s with decent cleavage!
All joking aside, when you are up against the clock, as you frequently are at the boarding gates - the worst offence in the book being a "Passenger Handling" delay - you do miss things.
....and on UK Domestic flights, both with BA and BMI, there are absolutely
NO IDENTITY CHECKS WHATSOEVER unless you check in with a human being. Apparently, we don't need them!