I’ve noticed this on software and websites but never that I can recall on anything else. The copyright date is a range, i.e. “1999-2004” or the like. What’s that all about?
Parts of the software were copyrighted in 1999, other parts in 2000, other parts in 2001, etc. In other words, new sections have been added as the software was changed.
You actually may see something similar with books, saying ‘Copyright renewed’, whenever there has been an update of the material (or more often, a new introduction or postscript added). In both cases the reason is to extend the copyrighted period of the work. Normally that is 70 years after the death of the author (per the De Bono-act in the U.S.A., and by European Directive over here), but for such ‘company’-published works without a specific author it is 70 years after publication (correct me if I’m wrong about this part in the U.S.A.)
I don’t think this is the case, since I see this on software created prior to the last year in the range.
Well, technically you can’t put a copyright date after the work is published, but I’m betting in this case, they are putting it on the package so that they don’t have to reprint the boxes when they release a version with bugs fixed next year. It wouldn’t affect the copyright if the date was wrong.
Features! Sheesh, RealityChuck, those were just unwanted features! 
It’s the shorter of either 95 years from publication or 120 yrs. after creation (e.g., if it wasn’t a publicly-available/published work). Applies for corporate works, anonymous works, works-for-hire, or pseudonymous works. 