I'm not sure I follow that hydraulics line of thinking
@Teebin - I don't doubt what you've heard, it just seems to contradict what's done in practice. I know Disney primarily uses hydraulics for its A-100's with compliance, and obviously Uni has flirted with the concept with Imhotep I. Hydraulics tend to result in smoother, more believable motion, just with greater maintenance costs.
Then again, there was that incident with Tiffany a few years back where she did spew something at guests...