As mentioned in the previous post if you compare the cover you may find that policies specifically sold for clients taking cruises may have additional covers that do not appear on a standard travel insurance policy. Whether they are worth paying extra for is something only you can decide.
If it is an expensive cruise then you may find a standard policy doesn't given sufficient cancellation cover but as long as the benefits of a standard policy are to your satisfaction then a dedicated cruise policy is not a requirement.
Hope this helps.