Accidental is not a valid reason, same as ignorance. Otherwise everyone could just say they accidentally committed a crime. That necklace accidentally fell in my purse, I was accidentally speeding, etc.
While this happens to be true in this specific case, as a general statement, it's misleading. It is true for copyright infringement because that is a strict liability tort, which means it doesn't require any particular state of mind ('mens rea'[0]).
Not all torts, and not all crimes, are strict liability. In your examples, if a necklace accidentally falls into your purse, that is not theft (in English law, anyway), as theft requires intent to deprive the owner of the thing[1]. Though once you notice it, if you decide not to return it, at that point it will become theft. Speeding, on the other hand, is strict liability (again: in English law, I don't know about US), as are most minor regulatory-type offences where it'd be difficult and impractical to prove intent.
(Also note: tort != crime. Copyright infringement can in some circumstances be a crime, but this is a lawsuit: the company is suing the Navy; the Navy isn't being prosecuted).
[0] https://en.wikipedia.org/wiki/Mens_rea
[1] http://www.legislation.gov.uk/ukpga/1968/60
NB: IANAL (did law, but ended up going into software dev instead)