1) You can sue anyone for anything. The US does not have a "loser pays" rule, though frivolous lawsuits can include attorney's fees.
2) Class action lawsuits are very profitable for lawyers when they win. They need to convince a jury of 12 people who couldn't get out of jury duty that "Big Corporation" was wrong. They get a percentage of the total judgment.
My guess is that some lawyer will pick this one up. They'll sue Amazon based on "common sense" and Amazon will realize that a jury isn't going separate a "book" from an "e-book". The plaintiff's lawyers will equate it to removing a book from your bookshelf in your house.
Amazon will argue commas in their TOS or Amazon will settle. On top of it all, Amazon demonstrates why I purchased a netbook instead of a Kindle for my e-book reading pleasure ... and why I don't buy e-books that I can't remove the DRM from.