It would be extremely nice if Jira maintained a name field for every status (or workflow step) and automatically put into that field the name of the person who caused the issue transition to the next step (which might have been a member of a group and not necessarily the asignee at the time of the transition). That would provide a complete and very nice audit trail. Those name fields should be referenceable as roles, e.g. the resolver, the closer, the verifier, etc. (see JIRA-11158)
There are certainly issues regarding what happens if an issue "cycles" through the workflow (visits a step more than once). I'd be happy with this field being overwritten in such cases, and containing the name of the last (most recent) person to cause the transition out of that state.