Perhaps under ideal conditions, but what are the long term effects? Are those engines still clean and reasonably healthy after, say, 300K miles?
There are also plenty of people doing extended oil changes with plenty of different reputable oils and wondering why they ended up with an oil burner at 100K miles.
To me, the risk vs reward of heavily extended OCIs just isn't worth it. I realize that type of thing is a game to many people and that's cool, but the way I see it, by the time you buy a very expensive oil and filter and have it analyzed a million times to see what the "right" interval is for your usage, you could have just changed it at, say, 5K miles and probably have a longer lasting engine for cheaper.
And if/when the extended OCI idea goes wrong, who will be out? Do you think the oil manufacturer or oil analysis company is going to replace your prematurely failed engine because they told you that you could go 20K miles between oil changes and you believed them? How much do you trust their advice?
I have a Blackstone report showing that my Amsoil SS needed to be changed after "only" ~6200 mostly highway miles despite that Civic calling for 10K mile OCIs on conventional oil from the 90's.
If I asked how long I should have run Amsoil SS in a low stress Civic engine that spends most of its life on the highway, how many people do you think would have guessed 6K miles?