Granted the US govt has there own (classified) encryption algorithms and as such that can't be replicated in a lab environment and requires access to the physical medium carrying traffic encrypted by said algorithms.
Which is why they do things like this : http://en.wikipedia.org/wiki/Operation_Ivy_Bells
Of course these days, it doesn't require nearly as much effort .. just a friendly phone call to AT&T (who, ironically, also built the devices used in the above).
Cheers, Michael Holstein Cleveland State University
