You are right (I upvoted you :).
Given current technology it is not reasonable possible to decrypt strongly encrypted data, however - there is strong evidence that using quantum computers this task is a matter of seconds. This technology is well defined theoretically already, just not reasonably implementable so far, which might be just a matter of some decade of time. In this respect, an encryption is the virtual equivalent of a safe, yes.
There is a complete other point I want to bring to your attention - our computers not only contain evidence, they also (might) contain lot of private and sensitive data, things you don't want anybody to know and where constitutional protection might fit since it's unrelated (I'm not knowledgable in the respective laws though, that's why I say 'might'), like a mental cache, and also hyper-links to other unrelated storages and networks (you can store much more virtual things on a computer than in a physical safe) - this makes a computer and it's disk somewhat different from a safe. It can potentially contain anything and the government would get access to a chain of homes like wandering through worm-holes because they were given one important entry code. This might affect the privacy of several other people, and they might not agree with that procedure. What is the law saying here? Are we going to be forced to use seperate computers for each task? rofl.