Tennis Scoring

Every time I was watching a tenis game I was wondering why they are not counting like all the other sports that I know..
In case you didn't know or didn't notice, in tennis, the counting is: love, 15, 30, 40, game. And then you start the next set.
My friend Google, helped me to find some answers.

Probably the counting is based on a clock face, and 45 was abbreviated to 40, probably because it is easier to pronounce. About "love" which means 0, there are 2 scenarios. It comes from "l'oeuf" French for 'egg' (The use of 'goose-egg' for a zero score is common in baseball), or it just means that the game is for love and peace in the world and stuff like that.

This counting system seems reasonable for that time, when the number 60 was considered "good" and "complete" number, in about the same way we consider 100 a "good" and "round" number. I still don't understand why they keep it and they don't make it 0, 1, 2, 3, 4. Actually, currently, you can use both counting systems, but the official is the old one.