I like the "Myth Busters" series, indeed
1. 40mA myth - the atmel says clearly in the datasheet the maximum current they guarantee as safe is 20mA
2. output resistance myth - the output resistance of a pin is not XYZ ohms, but it depends on many factors
3. your measurement myth - the only way how to measure the gate inrush current is with oscope during the rising/falling edges, voltage drops are not much relevant
4. 8us extremely high frequency myth - it does not matter how is the frequency of the pwm signal, but it matters how steep are the rising/falling edges, as the inrush current is largest during that time..
You may try to simulate the stuff with spice, I did it already in an another topic, but I will do it for you again..
(edges are 10ns):