http://www.patentspostgrant.com/wp-content/uploads/2009/11/Reexam-FAQ-Updated-11_30_09.pdf

don't know validity of article or except just fyi:

excerpt from above:

4. Why file an ex parte reexamination?

Answer: Consideration will vary for patent owners and third party requesters. Patent

owners should consider requesting reexamination when it is necessary to strengthen the

patent claims. This may include adding new claims to the patent which are narrower in

scope than the original patent claims but are necessary for licensing or enforcement

purposes

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The addition on new claims may provide the patent owner a basis to establish literal infringement rather

than having to rely on the doctrine of equivalents to prove infringement