I'm curious how much is attributable to the hardware, how much is the software, and how much is simply the fact that no human ever touches it. In a previous life I worked at a CNC machining shop and we had an RS/6000. Everything you say about the AS/400 was also true about the RS/6000. It ran AIX and nobody ever had to think about it because it always worked. But AIX is vastly cheaper than IBM i, and they run on the same hardware now. I think it's worthwhile to examine whether IBM i is actually providing the stability or if it was the hardware + no human touching it the whole time.