After riding from Los Angeles to Portland Oregon one December many years ago I took a serious look at why I ride bikes. I realized I didn't have to prove anything to anyone about endurance or anything. I ride for the pleasure of it, and riding in the winter, freezing my ass off, worrying about black ice, road closures, visibility and numerous other things isn't fun.
I have ridden the interstate, but in those cases it was a transportation issue, not a pleasure thing, and speed was of the essence. That's different. But normally I take the back roads and make it fun.
I won't be doing the Iron Butt either - just does't sound like fun to me!