Most likely not warpage but uneven material transfer aka hot spots.
Have you recently had a hard braking scenario say a panic brake from speed to avoid a ticket or obstacle?
As for warping you would have to have them really hot, pull into a car wash and hit them with the pressure washer. Its where the water doesn't make contact that will aid the distortion. If warped you will feel the vibration all the time, not just when braking.
For the average driver its not too much a concern or common to get pedal pulsation. But for spirited driving brake jobs they need to be more carefully done.
Not many people take the time to clean the rotor and hub mounting faces before assembly, much less use an indicator to measure for run out which should be no more than 0.002".
The more run out you have the more likely and severe you will get hot spots under spirited braking.
The above and/or in combination without proper pad to rotor bedding to apply an even film of material transfer will have you hot spotting also.
For the average Joe just slapping on new rotors and pads is OK. But if you like myself occasionally push towards the limits of your brakes some care and guidelines needs to be practiced.