There's a difference between time and events. Marriage anniversaries are counting time, just like the anniversary of TwinTurbo.NET. A 1st wedding anniversary means the couple has been married for one year; a 5th anniversary means 5 years. The 10th anniversary of the Gumball 3000 is the 10th event. The measurement is different but the word anniversary the same when describing time that has passed and number of event.
I love elitists who aren't really elite in any way... they amuse me greatly.