I would doubt it's your brake pads.. Mostlikely dust (Clean um, scuff um and whalllllla... and the life expectancy for the pads them self's are most likely going to be longer that your Rotors... (That sucks..... I Know).
I just replaced my front pads at 100k. I could have pushed it another 10k or so, maybe 5k. I had a nice weekend and a brother-in-law to help so I put pads on all around. The rears were about 3/16" but I wanted to replace them all at the same time. I went with Performance Friction and and not totally pleased with them. The rears were newer cuz I had to replace a left rear rotor after the caliper siezed and I didn't catch it in time. I replaced the LR rotor and both rear pads.
I was amazed that the front pads were as good as they were. I have been keeping an eye on them every 5,000 when I rotate my tires. 100k just seemed to be a good number for new pads all around.
I have pulled several loads on a trailer with no trailer brakes. The loads were substatial enough to give me a really good idea of how good the pads are. I did some really hard stops just to see how they did. The pads seem to have to be heated up to work really well, though. Kinda like a race car. Anyway, I don't plan on swapping them out cuz I plan on trading my rig in on a new one soon.