Hmmm, I thought Vesta would have the ice, not Ceres. Science books used to say that Vesta was the brightest asteroid, the only one that can bee seen with the naked eye, when conditions are right.
Perhaps Ceres just has a very dark surface; also Vesta isn't all that round, probably due to the apparent impact event, so it would have more surface area per unit volume. :')
"Though they are never visible with the unaided eye, many asteroids are visible with binoculars or a small telescope."
http://www.seds.org/billa/tnp/asteroids.html