I agree that the frequency doesn't change. It's the timing of when the bullet leaves that's affected by seating depth.
Regardless, seating depth is extremely important in tuning a load to the rifle. It often makes a greater improvement in grouping than minor differences in powder charges.
People are like rifles. Some are tried and true, having great eyes, personality, and fun to be with. Others never seem to hit the mark with you. Still others go off half-cocked. Still, it's nice to know most of them.