Just to add my $.02, since collecting safes are a hobby of mine. You are correct, there is a HUGE difference between fire-resistant safes, and media safes, in the way they protect the contents, the quality of construction, ratings, and most of all, price. Either way, I would STRONGLY recommend everyone to get some sort of safe, even if it's not optimal, it's still better than nothing.

Most all retail fire safes use some sort of gypsum or drywall lining, which releases moisture to raise the humidity level inside the safe during a fire. This effectively keeps the interior temperature down below the 350 degree rating for a certain length of time. And most everyone that's read Ray Bradbury knows the ignition temperature of paper is 451 Farenheit. The problem is as you mentioned, media is destroyed way below that temperature. Also, there doesn't seem to be consistant standards for fire ratings, some rate up to 1700 degrees, some more, some less. I'm not sure how hot a normal house fire gets, so who knows how accurate the ratings are.

Media safes are much, much more expensive for the size, but are rated to keep contents below 125 degrees. They do it by using massive amounts of insulation, which makes the safe much larger and more expenisve for the same interior space. Also, neither one of these are really rated for theft resistance, they do a pretty good job, but for that you'll also have to look for a TL rating.

I'm guessing placement of the safe is also an issue, I've heard certain areas stay much cooler during a fire, such as next to an interior brick wall where it won't be exposed as much. I haven't been able to find any studies to support this, just ancedotal evidence.

The other things you need to look for are a good seal. Not only will it expand to seal it during a fire, but it also keeps water out. Having gone through a house fire before, it's not just the fire that will do damage, but the fireman also. When are trying to put it out, they can cause just as much, if not more damage than the actual fire. I actually take the layered approach, and keep a smaller safe within a larger safe. I can't say for sure how well it works, but if it protects the contents against the heat for just a few minutes more, that might make all the difference between saving it and losing it.