There will always be factions on either side of the ski glove vs. ski mitten debate and warmth is not the only battle ground. For instance, dexterity when skiing can be just as important a factor as warmth. No matter how warm your fingers may be, if you are learning to use poles for the first time, mittens will only make the process more difficult.
A novice skier needs flexibility in almost every body part in order to be successful on the slopes. By wearing gloves instead of mittens, a newer skier will be able to grip the pole and adjust his or her hand to the poles movement down the mountain. And a god grip on the poles can be the difference between going feet first as opposed to head first down the mountain!