I would just like to post here some responses I have gotten in the comments section of this post http://readingbookwatchingmoviesandmore.blogspot.com/2008/05/super-heroes-is-trademark-jointly-owned.html
Yep, it's true, and has been for a few decades. It may be used as a generic term to a certain extent, but not so much as to make trademark inapplicable.
Back in 2004 (when an indy comic "Super Hero Happy Hour" ran afoul of this trademark) Todd Verbeek wrote an interesting piece on the subject at http://briefs.toddverbeek.com/super-heroes%C2%AE-a-trademark-of-dc-and-marvel/
which is interesting reading.
Most dictionary definitions and common usages of the term are generic and not limited to the characters of any particular company or companies.
Nevertheless, variations on the term "Super Hero" are jointly claimed by DC Comics and Marvel Comics as trademarks. Registrations of "Super Hero" marks have been maintained by DC and Marvel since the 1960s. (U.S. Trademark Serial Nos. 72243225 and 73222079, among others).