I'm not a fan of cast spindles, but there's another line of thought on this. Cast spindles that I've seen are not completely cast, but rather a composite of two different metals. The part that failed is not likely cast. The spindle snout is machined from steel and installed in the spindle main structure. Looking at the picture from the link posted, the grain is unlike what I'd expect to see in the characteristics of a casting. The fracture appears to be more from incorrect heat treating; something that could occur in a forged spindle also. Even though this may be an anomaly, I wouldn't buy a cast spindle if a forged one were available.

Bob