They actually pull too much cable. Cantis are drawn into the rim from an angle (as opposed to straight on with a v-brake) so require more cable pull for the pad to travel the same distance.
Using canti levers with v-brakes provides a rock solid, dead feeling with about 1/2 the lever travel.
I may actually get away with it, tried some ss5 type levers with vee's last night and they feel pretty dead, however the XT levers are servo wave, which was designed to pull the brakes on quickly and then give some modulation (if I remember the dealer manual from '93 correctly) so that should give some feel to them. Will let you all know once I try it as this may be a good thing for all of us! Retro levers and effective brakes