I would agree with you that professors should be able to publish their own articles on their own websites, but I can completely understand the journals' position.
Most of these journals are run on a shoestring budget by other academics who volunteer a ton of time. Any revenue from the reproduction of their content (including revenue from online subscription services like LexisNexis) is critical to their ongoing existence.
There are two "invasion of privacy" claims that may be applicable here:
1. Public Disclosure of Private Facts
To establish this claim, one needs to generally prove:
a. The defendant publicized information about the plaintiff's private life;
b. The publicity would be highly offensive to a reasonable person;
c. The matter publicized is not of legitimate public concern; and
d. The plaintiff suffered an injury as a result of the defendant's disclosure.
2. Intrusion on Seclusion
The elements of this cause of action are, generaly:
a. The defendant intentionally intruded on the plaintiff's solitude, seclusion, or private affairs;
b. The intrusion would be highly offensive to a reasonable person; and
c. The plaintiff suffered an injury as a result of the defendant's intrusion.
In the case of the Governor Sanford, since he is a public figure and adultery is against the law, the emails are most likely fair game because they would be considered "legitimate matters of public concern". That being said, there could still be a crime if the emails were unlawfully "intercepted" or if somebody hacked into his email account.
As for the 11 year old boy, publishing his private profile can certainly constitute both a public disclosure of private facts, as well as intrusion on seclusion.
My guess is, however, that Gawker had a clause in its terms of service in which the 11 year old boy "consented" to this type of disclosure. The fact that he is only 11 years old may raise an issue as to whether or not he can consent to such a disclosure...