Everyone's focusing on the fact that Snowden claims he is torture-proof, when in reality he never said that. He said that he "cannot" be tortured into revealing information he is protecting.
For example, Glenn Greenwald may hold a private key which must be used IN CONJUNCTION with Snowden's key to decrypt the information Snowden has. It's possible/probable that Snowden does not have access to the secrets he protects without Greenwald's key, as well as possibly many other keys. He may have a network of people he's made part of the group such that any two of them plus Snowden can decrypt the information, but Snowden himself can't without two keys plus his own, and he could make it such that his key is required in the group of three to decrypt. Hopefully someone else here can provide the name for this kind of encryption (something like n-key encryption, it's escaping me currently) and a link to how it works, but this is all very sound and entirely doable from a math standpoint.
So no, Snowden himself isn't torture proof, but his security is, if he's doing something like what I outlined above. They'd have to go after Glenn Greenwald too, or whoever else is involved, before gaining access to the intel.
Edit:
This link[3] might explain it slightly better, but I once read a great primer on the topic, filled with examples and was pretty simple to understand (the layman could grasp at least the concept). I'll add more links as I find more info.
[1] http://en.wikipedia.org/wiki/Secure_multi-party_computation
[2] http://www.iacr.org/archive/eurocrypt2001/20450279.pdf
[3] http://en.wikipedia.org/wiki/Threshold_cryptosystem
[4] http://www.tcs.hut.fi/Studies/T-79.159/2004/slides/L9.pdf
[5] https://www.cs.cornell.edu/courses/CS5430/2013sp/L.SecretSha...
(thanks ##crypto for the help!)