I've experiended the same at XC race: good climber doesn't always descending well and vice versa. In my understanding Enduro should combine good climbing and descending abilities. In Wisconsin's defense I'll say that riding in Levis Mounds, for example, ain't easier then many West Coast trails. Climbs are steep, sandy and technical.
I can see another reason for XC guys being slower on downhill: bike setup. Steep geometry and high seat make it difficult to go fast. Wheels and tires are lightweight flimsy but fast rolling, not made for charging downhills like on a trail bike. If I was racing I'd think twice about charging at full speed on downhill and wrecking my bike before finish line.
Whit that said I wish one day I can climb like those racers and flying downhill like a pro. :) For now I just riding for fun and for free