Cold Reboot Attacks on Disk Encryption

You missed the point. If you know that a key exists somewhere in RAM, it is fast and simple to
read a key's worth of data starting at every byte in the system, and attempt a decode of every
one until you find one that works. Brute force with one giga of attempts. No knowledge of OS,
language, data structures, or app code is required, aside from knowing the encryption
algorithm and key size (which is usually easy to find). Dead simple. And quite effective.

Splitting the key, or having an encrypted key with its key elsewhere in RAM would foil that
attack. At that point, the cracker would have to know something about the specific app and
craft a custom attack, which makes the attack quite a lot more difficult/expensive.

It's like locking your car so the stereo thief breaks into the unlocked car instead. It won't
block a highly motivated/funded attacker, but will keep out some script kiddies. If the cost
of splitting the key is near zero, it might be a good benefit/cost tradeoff.