Alex--
Could it also be that English--especially American--has/uses more slang in every day speech than speakers of other languages. Speaking from an American perspective, the Canadians, British, Australian, New Zealander, and other parts of the English speaking world use less slang than the Americans. Even the slang has different meanings in each English speaking country:
Mob is a gang of people in U.S., but is a herd of Animals in Australia. In Britain, To Knock up means to give a wake up call, while in America, it has a TOTALLY DIFFERENT meaning.
