One uses "à tous et à toutes" just to emphasize the fact that one is wishing a happy New Year to both men and women. Just as you would say "Bonjour à tous et à toutes"... or actually "Bonjour à toutes et à tous" if you're a real gentleman (Ladies first). Frank, where's your gallantry? ;-)
(just kidding)
Anyways, it has exactly the same meaning as "Excellentes fêtes à tous !".
Et à ce propos : excellente année 2010 à toutes et à tous de ma part également ;-)
In English we say 'Ladies and Gentlemen'.
We don't say 'Gentlemen and Ladies' simply because 'Ladies first'. So naturally we respect ladies.
Most of the time I listen to the French TV; it is TV5.
They say 'Bonjour à tous'.
So 'Bonjour à tous' includes mail, female, email, etc.
However, I am not good at grabbing each and every word when a native Frenchman speaks.
They speak very fast and as you know I have a smattering of French.
I always struggle to understand what they say and keep one of my dictionaries at hand. Do they say 'Bonjour à tous' OR 'Bonjour tous et toutes' ?
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For me the English word 'gallantry' is a formal or rather old fashion one.
We could say gallant soldiers, for example.
However, I am not a native English speaker like Pam.