Google has removed the @id mentions in the site name documentation calling the use of @id "unneeded." If you compare the old version of the page to the new version, you will see the example code that shows @id lines were removed.
Google wrote that today, August 2nd they have "removed unneeded mention of "@id" in the site names documentation."
Here is what was removed, these three @id lines in the sample code on this page:
So if you have those in your code for site name markup, you can remove it.
Forum discussion at Twitter.
