There might not be strong enough cases against some of the prisoners in Guantanamo, so holding them there, under their special status, allows the gov't to hold onto them without having to go through all these bothersome limits on detention. Plus there's the argument that people in Guantanamo could be especially dangerous if re-released (not defending this).

There really isn't that sort of problem with Snowden. A videotaped, non-coerced confession? Hundreds of articles sourced by him? How could the facts be clearer-cut? Trials could begin immediately, the worst he could do is pull an Assange-style blockade in some embassy.