The decryption key doesn't construct data anymore than the combination to a safe constructs the papers inside it. The data exist independently of anyone's ability to read them.

I disagree. It is entirely possible to have a set of bits the can be 'decrypted' with different keys producing different results. One key might produce a set of cartoon pictures, another might produce financial records. The simple safe analogy seems to break down around this. Only one key unlocks a safe. Every key can be used to decrypt something that is encrypted, but unlike a safe, its not guaranteed what goes in comes out. I would argue that the data only exists if it can be read and that providing a mechanism for reading the data is establishing the existence of the data.

What does that mean for XORing your data with an equal-sized chunk of truly random data (pulled from, say, http://www.random.org/ )? From an information standpoint, the data is gone because the result is also truly random, and doesn't exist any more except in the combination of the output and the key.

The purpose of encryption is to obscure and prevent access to data, not store it.

Under that definition encryption equals /dev/null. It's a way to store data while limiting access to said data.

That's all a matter of perception though, no? Encryption is capable of storing data, therefore it can be used legitimately to do that. Just like most people use fans to cool people down during the summer, but people also use fans on large semi-rectangular pieces of metal to create hovercars.