Yes, I always wonder.. when you say that your salary is $10k per month it should be just that - basic and perhaps some allowances but I think many big cannon tend to take it as their annual salary divided by 12.

Eg I am on a 17-18 month package for the past 6 years and my basic is relatively low. Heck, even my wife is earning more than me per month but my annual package is much more.