I'd love to play Frost. I started a dwarven mage to play frost. Found the perfect mog for him too (increases dps by 20%, it is known).
But arcane gets Alter Time, Slow, and even Mass Invisibility if you spec for it. I'd really want to play Frost or fire, but the defensive options of arcane are just too good (and fun actually) to pass up.
I dont get why they didnt give all specs Alter time at the same level. Well, not entirely true...I kinda get it, the designers at blizzard arent exactly the "creme de la creme" anymore. More like already expired yogurt that you should have trashed from your fridge a long time ago.