A creature of the Cold subtype carrying around a flaming broadsword is either stupid or insane. About like a lycanthrope carrying around a silver weapon: you might find it useful when fighting other lycanthropes, but if you get disarmed, you're probably going to die by your own blade.
I dunno, man...a lot of creatures have venom that the creature isn't immune to. Classically, the medusa wasn't immune ot her own gaze. In "survival of the fittest" terms, think about nuclear development...it's the one thing that can severely cripple an entire nation, and yet the risk of them being used against us is one of the very reasons we develop it. The way we prevent that is security -- in D&D terms, perhaps the chained gauntlet that makes it impossible to be disarmed.
I know the chance of being disarmed or having that item stolen doesn't really stop the party wizard from grabbing a wand of
magic missile, and it doesn't stop the party fighter from picking up a
frostbrand (even if, let's say, his party cleric is a cleric of a fire god and cannot protect the fighter from cold damage....for some reason). I don't know very many rangers who don't pick up a bane weapon for their favored enemy, even if their favored enemy is the same type they are.
If they *don't* use the ambient fire powers to their own advantage, then the first creature who does (through perhaps a genetic glich, or a lost population recently awakened, or maybe an adventurer) is going to run rampant over everything.
This isn't, of course, to say they wouldn't use frost, or that other energies wouldn't play a part. Indeed, as argued above, cold energy may simply be
easier to gain in cold environments, making it more common. But depending on where your critters live, they should be aware of and make good use of fire, too. I mean, they use weapons and armor made of steel, unless they have some cold forge, they're going to need to master the controlled use of fire. And once they have that forge, that volcano, that geothermal vent, fire should come pretty easily, too...need a salamander scale and frost giant blood? Well, hop on down to the forges, where salamanders sometimes creep through, and then head up to the glaciers, where the frost giants live.
Frost will definately be used, maybe even taken for granted. But fire's not going to be uncommon, especially among the more intelligent and powerful creatures. Much like a nuclear arms race, they're going to be pouring rescources into the development and mastery of fire, because it is the most effective weapon up there. They're not going to neglect frost, and frost will probably definately be more common, but fire is an important rescource, and for them not to make use of it is just silly superstition on their part. I wouldn't be surprised if bog beasts were affraid of it, but I'd be mighty surprised if frost giant sorcerers didn't specifically undergo practices to hone fire powers. And given the alignment of most of these critters, I don't think that any arms race would be a peaceful standoff, rather I think they'd be using it at every opportunity, even against their own people, using it to threaten, bully, harass, and keep themselves in power. They may even try to limit it at the lower levels -- if you need forge access to develop fire skill, the frost giant kings may outlaw such things, especially for the commoners. But by the time you're facing the top predators and the kings themelves, they should be breaking out the fire guns. Not all the time, mind you -- frost is still common, easy, and popular. But enough to make sure that any party preparing to fight an ice monster of this caliber with fire spells and effects is going to find their efforts seriously thwarted. Which will, of course, send them into using other energies.