Frost mages can do some sic damage too, the primary reason they do so well in Raids is fire stacks much better, say you have two fire mages, throwing up scorch and then spamming fire, the damage is exponentially increased. Most everyone already said everything; however, a quick note, I begin stacking +frost damage in my 50s in lieu of intel, then outlands offered +dmg to all spells as well as stam/intel crit rating etc. After a few levels my spell dmg and spell crit were pretty insane, compared to pre outlands, so on the PTR for patch 2.4, I had to see fire, as I was fire til 50 and LOVED it, usually two shot sometimes 3 before they hit me. I didnt realize how much I missed my elemental and how much I missed slowing everything around me down. On top of that, my winter chill, frostbite, frost nova shatter crits, even without shatter crits as my crit rating is getting over 20% so I crit VERY often, the FB crits go about 2300 (at around level 64 or so) give or take, when I tried fire with the same +dmg and +crit it was just a tad higher and didnt offer all of the nice features of frost. Add in Ice lance where it does triple damage to a frozen target, well...
My method is a double shot method when they are frozen, as you finish casting FB do a fireblast, almost like doing two shots at once and youll see a bunch of big numbers explode before your eyes :)
I actually like and recommend leveling fire, then switching early 50s (WE FTW)and continuing on to 70. For me, once I craft most of my T5 gear, I will prob respec fire, but the control of elites, in dungeons, and solo play, plus the pure damage that frost is actually capable of, its def PVE and raid viable. And if you like PVP, well thats open to you as well.