Interestingly, the canned version uses a different formula than the fountain version (http://www.mountaindew.com/about_dew/product_info/dmd.php).  The fountain version does contain saccharin, which was a surprise to me ("Where's the Tab key?").

The new canned formula still has aspartame, but it also has acesulfame potassium and sucralose.  Sodium benzoate has made the ingredients list, as well... and not as a replacement to potassium benzoate.  Maybe they want to extend that "freshness date" a ways?