I never knew this rule existed either. Quite a few years ago when I worked for an airline I had the opportunity of visiting Buenos Aires briefly. Not knowing the language and only there in a work capacity I only spent spare time in my hotel room (quite sad I know, but I was young and a bit scared to venture out too far!) Anyway, in Buenos Aires they have a whole TV channel dedicated to Tango, it was bliss, just watched this the whole time I was there really.
I remember them talking about the history of Tango and that in Buenos Aires in particular, the early 1900's had a surge of 2million immigrants arriving from Europe (Italy & Spain). Many were single men, hoping to earn enough to return to Europe, or bring their family or buy a bride from Europe. A poor, desperate, male population bred crime, brothels, gangsters, and the tango!
Men danced together - there were few women, but tango inevitably moved to where they could be found - in the brothels,
and it is said that the women could chose their clients by their dancing skill. The man had three dances to prove himself!
Maybe the men only being allowed to ask nowadays is a sign that they don't think you've originated from a brothel!!!
Bex