You're actually looking at an IC or Interchangeable Core. After 5 years of locksmithing I still haven't figured out why these cylinders are so difficult to pick.
They can have between 6-7 pin stacks, and virtually always have mutiple shearlines because of masterkeying and the extra pins to move the control bar (which holds the cylinder in the knob) which in theory should make it easier to pick, however, like you've pointed out, these cylinders are stiff to pick.
Here's a tip, though, make sure the lock is lubed thoroughly as quite often these locks are generally assembled with graphite which tends to make them sticky after years of use. Oh, and make sure you're turning it in the correct direction, else you may accidently remove the cylinder.
*insert witty comment here*