I gave this a lot of thought. My guess is in order for the Amsoil filter to last 25,000 miles it isn't filtering as well as a Pure One or Mobil 1 filter. It is not trapping the smaller stuff. Now some might say the smaller stuff is harmless, at least that is what I'd say if I was selling those filters. Me I'd take the filter that traps the most stuff, and change it more often. No point in filtering out big stuff, leaving small stuff so the filter will last longer.
OK flamers, torch me.