To make the example more clear:
1. Let X = illegal file
2. Let Y = completely random bitstring of same length as X
3. Let Z = X xor Y
4. Post Y on one server, say a google blog. Post Z on another, say a wordpress blog.
Now observe the following: Y is a totally random string, so clearly it contains no information about X. What about Z? Well think about it: if I take some fixed string X and XOR it with a totally random string, what do I get? I get another totally random string. So Z is also a totally random string, containing no information about X either.
So now we have two servers both storing totally random strings. Clearly, neither is illegal alone. But their XOR is illegal. Who commited a crime, other than the uploader?
Does either of them have a purpose other than being able to be recombined to reconstruct the original illegal file? If not, what's to stop the courts from ordering both to be removed? (Obviously if one of them does have a purpose other than being able to be used to reconstruct the illegal file, the other one must contain the information about said illegal file; due to the way the two files have to be constructed it's impossible for both of them to have been created for another purpose.)