That's really all it could be. ........
...........Rotor thickness and/or un-eveness isn't going to be felt by "extra" travel in the brake pedal. You can feel it when actually stopping by either vibrations in the pedal, or worse, vibrations in the car. But the pedal travel distance isn't really effected either way.
I have to disagree. Taper wear on the rotors (rotor thinner toward it's outer edge, typically due to the greater speed with which the rotor passes between the pads further out) and taper wear on the pads (either thinner toward the outer edge of the pads, and / or thinner toward the trailing edge, parts of the pad that run hotter than toward the inner edge and leading edge) can cause unwanted piston movement before the pads fully 'engage'.
In either case there is a gap between the pads and the rotor surfaces, i.e. the thicker parts of the pads and / or rotor will be in close proximity to the rotor and / or pad, leaving a gap where the components are thinner.
When the piston moves good contact will first be made where the components are closest (thickest), but before any real pressure can be exerted the piston must 'tilt' in its bore in order to exert force across the whole piston (and thus the pads). This movement is manifested to the driver as a slight delay in retardation, and most obviously as excessive pedal motion.
The piston doesn't remain tilted when the hydraulic pressure is released, but rather is partially retracted and 'untilted' by the hysteresis in the elastic piston seals. When the pedal is re-applied the clearances must be taken up again.
Reluctance for a floating brake caliper to slide on the pins (i.e. full or partial seizure of at least one pin) causes strains and flexure in the caliper bracket, which is manifest as pedal motion (and often as one pad wearing much more than the other).
Typically one pin will be more seized than the other, so as pressure is applied the caliper will slide more on one pin than on the other, resulting in the caliper becoming tilted, especially as the pads become more unevenly worn. Note that this creates elastic
flexure in the bracket, so as pressure is released the bracket resumes its 'as manufactured' shape, which pulls the pads back away from the rotor.
I've encountered all these problems when chasing down the cause(s) of excessive pedal movement. I'm sure that a well known search engine will easily find pages explaining all this more fully.