... that shows both the old and new versions
Yeah, I get the same page. But it only compares the changes to the prior revision. Let me give you an example.
We're using revision heavily when translating the support pages to german. Sometimes two to three people are working on a page. So the revision module might look like this:
User 3, 4 days ago (Juni 3rd, 2013 @ 20:36:16)<br />
User 3, 4 days ago (Juni 3rd, 2013 @ 20:12:45)<br />
User 2, 5 days ago (Juni 2nd, 2013 @ 16:12:08)<br />
User 2, 5 days ago (Juni 2nd, 2013 @ 15:53:36)<br />
User 1, 6 days ago (Juni 1st, 2013 @ 08:14:17)<br />
If I post a link https://blahblah.wordpress.com/wp-admin/revision.php?revision=501&action=edit in our teamblog and user 1 clicks on it he/she only sees the changes between the current revision of user 3 and the other one by the same user. If he/she wants to see the changes between the current revision and his/her own (user1) revision you have to enable the checkbox on the upper right and use the slider above to make the comparison. This means a lot of clicking.
Before the changes the urls looked like this: https://blahblah.wordpress.com/wp-admin/revision.php?action=diff&post_type=page&right=297&left=812
You see? Two revisions within the URL. By simply one click you could see a comparison between the changes of user 1 and user 3 without the need to do all the extra work on finding/configuring the revisions yourself.