Um, you just made the point of the article. The ability to make arrests for non-federal crimes like State gun laws. The Governor has no one else to call on to make those arrests so they need a federal agency like the SS to be able to do so.
Um, you just made my point - people need to read the legislation. They can make an arrest only if they witness it happening or about to happen, or if asked to do so by a Colorado law enforcement official. You would no doubt find similar laws granting similar permissions to FBI agents, BATF agents, and other federal law enforcement officials.
And why wouldn't the Colorado authorities be enforcing state laws?