I hear what you are saying, it's fine for me and all the Lexus owners I know, but NOT for all. Yes, we haven't had engine seizures and oil sludging, no kidding. And we know what happened when Toyota dealers tried to deny oil sludging claims, Toyota got reamed and paid millions in the end. But to your point, it is a good historical example of how they unsuccessfully attempted to "stab in the back" good customers. And it's not certain they want to go down that PR disaster and expensive road again.
Like you I have years of experience with the 2 brands as well as other premium brands, not to mention internet forums.
But I agree, for those that feel its a risk and cannot afford the extremely low risk they should follow memo by all means, keeping in mind new development below since memo was published. Therefore it is not fine for all, per memo.
Now it's a non-issue (not that Lexus is making it a issue, it is certainly something to discuss on Internet). Because Lexus now has 10K intervals with approved synthetic on 2013 GS 350 with same engine as IS350. Good progress and expected from a leading premium brand. It's not so much a cost issue for owners, more of practical use of time and not wasting resources.
Again to repeat, it's not fine for everybody to casually change to 10K intervals, see above.