I agree with Chris Ellis (whoever he is).
Most successful bracket racers (who compete in the NHRA divisional events every weekend and make it to the annual bracket nationals events) have cars with small block V8's, 2 or 3 speed automatics (with air or co2 shifters), 2 step rev limiters and transbrakes.
Their ET's are usually +/- 0.002 seconds and reaction times are extremely good.
For any Turbo car to be as consistent, it would have to leave the line at the exact same boost and rpm every time. That is difficult to do when you are trying to build boost while staging.
I've tried bracket racing without building any boost at all but as a result my reaction times were horrible, because it takes longer for the car to get moving and untrip the beams!
And as someone else already stated, weather has a bigger effect on turbo cars than n/a cars. Even the time between rounds can effect the performance of a turbo car because of the underhood temperature, temperature of coolant, oil, transmission fluid, intercooler, etc not cooling off the same between rounds.
I'd like to see the types of cars that have placed first in all the bracket classes at the buick gs nationals since the event started - I bet 90% or more of the final round winners are naturally aspirated.