A SOAP API method using an issue id seems odd

Looking at the new methods in the SOAP API for the 4.0.0 beta1 there is one method that seems odd: getResolutionDateById(String token, Long issueId)
Why would I want to use the Long issueid parameter for anything? Finding the issue id (as opposed to the issue key) is hard. What's the purpose of adding this method to the API?

Interface com.atlassian.jira.rpc.soap.JiraSoapService

Added Methods from 3.13.1 to 4.0.0 Beta1

boolean addBase64EncodedAttachmentsToIssue(String, String, String[], String[]) An alternative mechanism for adding attachments to an issue.
void deleteProjectAvatar(String, long) Deletes the given custom Avatar from the system.
RemoteIssue[] getIssuesFromFilterWithLimit(String, String, int, int) Returns issues that match the saved filter specified by the filterId.
RemoteIssue[] getIssuesFromTextSearchWithLimit(String, String, int, int) Returns issues containing searchTerms.
RemoteAvatar getProjectAvatar(String, String) Retrieves the current avatar for the given project.
RemoteAvatar[] getProjectAvatars(String, String, boolean) Retrieves avatars for the given project.
Date getResolutionDateById(String, Long) Given an issue id, this method returns the resolution date for this issue.
Date getResolutionDateByKey(String, String) Given an issue key, this method returns the resolution date for this issue.
void setNewProjectAvatar(String, String, String, String) Creates a new custom avatar for the given project and sets it to be current for the project.
void setProjectAvatar(String, String, Long) Sets the current avatar for the given project to that with the given id.