That said, let's remember this about Cassel:
He sat behind Tom Brady for three years after being drafted in the seventh round in 2005 by the Patriots, attempting a total of 39 career passes from 2005-07 in mop-up duty. By the time he made his debut as a starter for an injured Brady in 2008, he was 26 years old. He had a good year in New England that season, a mediocre season in KC the next season, a very good year the season after that and two mediocre-to-bad ones (with injuries) following that.
Ponder, who just turned 25, is a year behind where Cassel was (third year vs. fourth year) in his first year as a starter and a year younger as well. While 2013 should definitely be viewed as a judgment year for Ponder, and Cassel is certainly a more capable backup than the Vikings had in 2012, Minnesota is correct to say Ponder is its starter and Cassel is its backup. Cassel is more accomplished, but only by a function of age and experience. It is reasonable to expect Ponder to outperform Cassel as he gains the age and experience necessary.