You know, I keep hearing about how the crank case vent bottle is the culprit for all the crud on our radiators, but I completely disagree. First off, I can't see how a fan that sucks air could spit it back at the rad. Second, my 1997 was a V8 and had the exact same crud buildup on the radiator as the CTD; as far as I know, the 5. 9L gasser has no crank case vent bottle.
I think it's just 100,000+ miles of crap flying into, and getting sucked through your radiator, as you're flying down the road.
Either way, Glenn you're right, it's one less monkey on my back, knowing that it's clean now.