Brock was replaced with Tracey, because those working on the Anime, were afraid that people in America would be offended by Brock's design, specifically the squinted eyes. So they replaced him with a stereotypical white Anglo-Saxon Male, to avoid any scrutiny. But they brought Brock back for the Johto Arcs, because of his popularity, and the simple fact that no one had a problem with his design. Although this was only stated in an interview wit former Director and Storyboard Artist Masamitsu Hidaka.
But the credits are followed by a free Frogurt.The Frogurt is also cursed.