Seen the terms "copyright" and "trademark" thrown back and forth on this string and thought I'd pass along a helpful link from the home office: http://www.uspto.gov/trademarks/basics/index.jsp
. In this case, we are talking trademarks.
As for trademarks themselves, "the registration is valid as long as you file all post registration maintenance documents. You must file a “Declaration of Use” between the fifth and sixth year following registration. In addition, you must file a combined “Declaration of Use and Application for Renewal” between the ninth and tenth year after registration, and every 10 years thereafter. If these documents are not timely filed, your registration will be cancelled and cannot be revived or reinstated. For more information see Maintain/Renew a Registration."
Depending on which names fell out of active use, it is often easier for Hasbro to register a new trademark such as "Autobot Hound" than attempt to regain use of an expired mark registered by another entity. The more generic the word is, the harder it is to trademark.