There is no "world wide" IQ test. All tests are specific to cultures/language groups and normed for that culture.
The 100 is the average score (by design) on the Wechsler IQ test and the Stanford-Binet IQ test, 2 commonly-used tests in the US.
You are correct - and I have to say that it's nice to have your input concerning this subject. Many people don't know very much about assessment, and there's a lot of bad information floating around that unnecessarily confuses the issue.
Thanks!