Wow. I wonder how the respondent came across this really old article. Glad they did, since it remains accurate.
In any case, I think 'hellocsharp' is trying to read the term "subpoena attack" as something less literal than it means. A subpoena attack is exactly what it sounds like: someone gets a subpoena to search or seize the servers that provide some service, such as anonymity. I suppose nowadays, in this era of warrantless wiretaps, that sounds quaint.
In general, some cryptographic design can potentially be attacked by a legal order to access the machines the cryptography runs on (some designs are resistant to this, others are not. A system like, e.g. Hotmail, presumably has no such resistance, and Microsoft will happily turn over all the information it has in response to a court order. Other systems, like the one I describe avoid letting the machine or its user having the capability of turning over (at least some) compromising information even if the user wants to.