Hmm, precession. Precession is where the force applied gets effectively applied 90 degrees in the direction of spin. The point was that if the spin axis is the pitch axis, then no force would be applied if the aircraft pitched, therefore there would be nothing to precess.
Methinks either my notes are incorrect when they say that the spin axis and the sensitive axis mean the same thing, or the chaps meant to say perpendicular instead of parallel. I shall take it up with the author.
Another idea (a rather bizarre theory I had which is probably nonsense and the product of a deranged mind), is that rate sesning gyros may operate in a similar way to ring laser gyros. That is, with an RLG a pitch would shorten the path of one ray of light and lengthen the other. Is it possible that a pitch would shorten/lengthen the path of the rim of a conventional gyro in the same way, hence enabling a measurement of rate or rotation? If I haven't completely confused you all, discuss!
TB