From another perspective, I don't have Frostburn, but I have seen, uh, real snow.
If I'm Joe Frosty the King of the Frost Giants, and my giant castle, carved from blocks of ice, resides in the center of a permanently frozen lake that sits at the base of a snow-covered mountain... flinging around fireballs just because I suspect that someone might come in from some totally different environment and not be expecting is not really a winner as strategies go.
Sure, it'll surprise those pesky adventurers who showed up to ruin my day, but the walls of my castle will be turning into slush, the icy surface of the lake isn't going to support my weight once that ice starts cracking, and a giant wash of heat in the wrong direction could conceivably cause an avalanche.
In the unlikely event that I found myself GMing somebody who played a frost giant but wanted to use a flaming weapon, I'd politely suggest that he wouldn't find it comfortable (like a good character wouldn't find an unholy weapon comfortable to use), just like I'd politely imply that while yes, many of the party's enemies are human, asking the human wizard to make a human-bane weapon for the human fighter to wield is not going to work.