You know what, I think the judges might well take ‘judicial notice’ of it (and have).

Anyway, let’s look shall we?
18 UCS §875(d)

Whoever, with intent to extort from any person, firm, association, or corporation, any money or other thing of value, transmits in interstate or foreign commerce any communication containing any threat to injure the property or reputation of the addressee or of another or the reputation of a deceased person or any threat to accuse the addressee or any other person of a crime, shall be fined under this title or imprisoned not more than two years, or both.

highlighted the appropriate section.

Wonder what Aussie law says. Let’s look shall we?
Let’s look at Section 415 of the criminal code of Queensland

415 Extortion
(1) A person (the demander) who, without reasonable cause, makes a demand—

(a) with intent to—
(i) gain a benefit for any person (whether or not the demander); or
(ii) cause a detriment to any person other than the demander; and
(b) with a threat to cause a detriment to any person other than the demander;
commits a crime.

Maximum penalty—

(a) if carrying out the threat causes, or would be likely to cause, serious personal injury to a person other than the offender—life imprisonment; or
(b) if carrying out the threat causes, or would be likely to cause, substantial economic loss in an industrial or commercial activity conducted by a person or entity other than the offender (whether the activity is conducted by a public authority or as a private enterprise)—life imprisonment; or
(c) otherwise—14 years imprisonment.
(2) It is immaterial that—

(a) the demand or threat is made in a way ordinarily used to inform the public rather than a particular person; or
(b) the threat does not specify the detriment to be caused; or
(c) the threat does not specify the person to whom the detriment is to be caused or specifies this in a general way; or
Example—
a threat to cause a detriment to the public or any members of the public
(d) the detriment is to be caused by someone other than the demander.
(3) A reference to making a demand includes causing someone to receive a demand.

(4) A reference to a threat to cause a detriment to any person other than the demander includes a statement that gives rise to a threat of detriment to the other person.

(5) A prosecution for an offence in which it is intended to rely on a circumstance of aggravation mentioned in paragraph (a) or (b) of the penalty can not be commenced without the consent of the Attorney-General.

(6) In this section—

threat includes a statement that may reasonably be interpreted as a threat.

Yep, looks like it’s basically the same, if not broader.
How about New South Wales?
Pretty much the same (don’t have a citeable reference, only the text of the 2007 Crime Amendments bill).

Now, if the threats in the lawsuits were CREDIBLE (they’re not, which is why they’ve backed off from pursuing them when a fight is made) or if it wasn’t made with Menace (defined as “A threat against an individual does not constitute a menace unless:
(a) the threat would cause an individual of normal stability and courage to act unwillingly in response to the threat, or
(b) the threat would cause the particular individual to act unwillingly in response to the threat and the person who makes the threat is aware of the vulnerability of the particular individual to the threat.”. They specifically dismiss cases against some people to avoid part b there) then they wouldn’t be extortionate, but they are. And the credible and menacing aspects were also why the courts wanted oversight of the letters.

So yeah, looking at the facts of the cases, comparing them to the laws, yep, ‘extortion’ still pretty much fits the bill.