Driddle said:
Sure, snow and ice and sleet are a the basis of nature in Icefell settings. But you'd think a few intelligent sapiens living in the area would hold WARMTH and FIRE in high enough regard to include them in ... oh, I don't know ... reference to deities and/or prestige classes and the like. Most of us hairy creatures are warm-blooded, after all. We like to keep our body temperatures at a certain comfort level.
But nooooooo -- it's all blue and white and freeze-your-tuchas-off icy beauty throughout the whole darned book. Gimme a break! What's up with that?
Apart from the fact that as others already said Frostburn is more a collection of cold-themed elements than the Complete Book of Cold Places, you are struck in a big false premise: that people worship what they like over what they fear (or that worship is triggered only by awe and respect and not by fear and opportunism).
It isn't thet simple; in fact it's often the opposite. Just look at the ancient RL mythologies: many deities are portrayed as petty, demanding or vindictive, yet they were worshipped all along; lightning, floods, earthquakes, plagues: name a misfortune and there was some god responsible for it.
In a way, it assuages fears. If I'm a primitive who doesn't know how and why lightnings develop and how I can avoid being hit during a storm, I feel more safe knowing that they aren't random, but fall according to Zeus' purposes: after all, I'm reasonably safe as long as I don't make him angry at me. Then I can go the extra mile and make offerings to the gods so that they don't harm me; but if I don't want to be struck by lightning I won't give offerings to the god of Grounding: that's just asking for trouble from Zeus; nah, I'll go directly to the source. This way, I turned an unexplicable danger into something I can control.
Now, let's say I live in a polar environment. Sure, fire keeps me alive, but it's also a tiny, pityful thing easily quenched by all snow and ice out there; in this landscape, it's the gods of cold that hold sway, not some upstart fire deity who finds herself sorely outmatched.
So when the adepts of fire knock at my door i'll say thanks but no thanks: no point in praying to your burning patron if it gets the much stronger and more pervasive cold gods breathing down on my neck in displeasure; I'd rather appease them so they don't send an avalanche to bury my puny fire.