A quote from a link wadams9 posted:

" If your going to use Eular angles (and every 3D package has them somewhere) your going to have problems with gimbal lock. The only advantage to using Eular angles is that they are much easier for an artist to read and conceptualize than a Quaternion Rotation."

Poser uses quaternions for animation interpolation when desired (menu Animation/Quaternion Inperpolation) to avoid some other problems Euler angles have, and you can access quaternion rotation values via Python.