Jumanji,
The real problem is that the issue essentially revolves around "quality", which is an impossible term to really apply rational credible numbers or calculations to. I think as has been said before on other posts and above is that certain things, casting of which are one, are sometimes very difficult to inspect or check prior to final hydro test which is where any faults would hopefully be found. By then nearly 2/3 of the schedule for the valves, which are often a critical time line item, will have gone and hence huge delay or costs ensue. Are good high quality manufacturers regarded the same - Yes I'm afraid they are, but until a long list of high quality items are established then it is not a fight you can win.
Clearly whoever the companies are, have their reasons, but they have that right and many are now very risk averse, especially for environmental damage and any failure of a component which causes damage or injures someone is a very big issue. As many of these companies work world wide, they can gather a lot of data about root cause of incidents and near misses, operational data etc and have decided that the lower cost of items such as valve castings is not worth the higher risk. Wait 5 years and it may go away.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way