Is rust and crud normal? I don't think it is "normal" if the system has been cared for properly, but it is certainly not unusual. As it turned out, I didn't have any rust or crud in my system and probably didn't need a flush, but I have flushed systems with plenty of that stuff in them. It can be the result of waiting too long between antifreeze changes or of running the system without antifreeze in it (the antifreeze has corrosion inhibitors.
In the case of my van, I've owned it since about 38K and I have changed antifreeze a couple of times though this was the first time I thought to flush it-- so it has always had the proper ratio of fresh antifreeze in it. The vehicles that had a lot of crud were a 94 ford explorer I bought a while back that had about 100K on it, and a Chrysler Sebring that had 120K on it-- who knows what service history either of them had, but from the looks, the antifreeze had never been changed in either.