Yes, it is in fact a blanket protection against having to give testimony.
The evidence is what it is, the court is there to judge it.
There have in fact been a few instances where judges have determined that providing a password does constitute giving testimony.
http://www.easterndistrictblog.com/?p=57
and older
http://mises.org/Community/blogs/crypto/archive/2007/12/18/c...
Where did you put your ex-wife's body Mr Johnson, we know you killed her? Just point at the map, you do not even have to say anything.
You could have cat pictures encrypted with passphrase A and incriminating evidence (that stands up to the best forensic analysis currently available) encrypted with passphrase B and they wouldn't know which is which, if they unlocked ALL the data, or what.
Truecrypt is AMAZING and anyone holding onto stuff that might get them into trouble (esp. w/ foreign gov'ts) should use it.