I found this:

What is the origin of the scoring system in tennis: love, 15, 30, 40?

The rules of the new game of lawn tennis were drawn up by the Marylebone Cricket Club (MCC) in 1875. Scoring derived from real, or royal, tennis, which had its origins in medieval cathedral cloisters. The name comes from the French habit of calling out tenez! (take this!) before serving. In real tennis, each exchange was worth 15 points, the score of 40 being an abbreviation for 45. Deuce is a corruption of a deux (meaning two consecutive exchanges needed to win). Love is either a corruption of l'oeuf (an egg) or playing not seriously but for the love of the game.
http://www.answerbag.com/q_view.php/341

...What concerns me about this is the deuce bit, not the love bit.
If you listen carefully to the French Open, you will hear that the first deuce is called as 'quarante �' (at least that's what it sounds like to me, presumably short for quarante � chacun - 40 each), rather than 'deuce'. A second or subsequent deuce is called as '�galit�' - equality.
SO if this all comes from the French, why don't they use it?