There is no changelog, because it would look ridiculous. You can see the changes by yourself, for example between 1.6.13.2 and 1.6.13.3:
http://plugins.trac.wordpress.org/changeset?reponame=&new=425973%40all-in-one-seo-pack%2Ftrunk&old=343245%40all-in-one-seo-pack%2Ftrunk
There were no functional changes, only the advertising on the plugin option panel has been changed and the “tested up to” value was increased.
I didn’t check the other updates, but I guess that there are many cosmetic updates just to get more downloads and spread the advertising.
