Eric Raymond: it was reported to me at the time that English has a richer technical vocabulary than any other language and is therefore simply a better tool for the job Or probably English is simply the most easy to learn.
In the early part of the 1950's in the USA, a game called "Violence Fight" was in vogue among mafia, reckless drivers and general businessmen. The "Violence Fight" was the game to struggle for "No. 1 Quarreler" with fighters who were gathered from all parts of the USA speaking boastingly of their strength. And of course a lot of winning money as well as the honor were given to the "winner".
(Example taken from here http://www.youtube.com/watch?v=MqnBWgrSt30). Other languages (e.g. french) just don't tolerate stuff like this.
For an example of a really easy to learn language, see modern Turkish. For various reasons (vacations and chicks) I've tried and failed to learn many languages. I came closest with turkish, vocabulary was my only sticking point. Ataturk simplified the language only 70 years ago, and it worked fantastically well.