The skates melt under your body weight the ice just a little bit to form a thin water film. In other words, the skates glide on a very small water cushion.
Ice skates have less surface area in contact with the ice.I'm a figure skater, and I think for most people who have never ice skated before, walking on frozen ice is easier, because you are use to...
I have ice skates.. because I am a figure skater.. Unless you play ice hockey, figure skate or speed skate there is not really another reason you would own some!