Technically it's not the same thing. Whether or not it is legally different is an entirely different matter - one that has not yet been resolved.

If the court decides that encryption is like a safe then, regardless of how impossible it is to open the safe without a key, the court can coerce you into decrypting your HD.

However, if the court decides that encryption is like a secret language that only you can translate (a more accurate representation of encryption, in my opinion) then they will likely rule that they cannot coerce you into decrypting the data.