Norseman,
It's obvious we haven't convinced you.
Let's take a typical scenario:
A tire manufacturer has an abbreviated line of tires strictly for OE usage. Knowing that the OEM's are going to go after rolling resistance, and anyone who would be purchasing these tires is doing so because it is the same tire that came on their and the purchaser doesn't really care what the rating is, the tire manufacturer will assign the UTQG numbers conservatively and have one number to cover the entire line. That makes it easy when they go to publish their marketing booklets - these tires will be near the end of the book, and not highlighted at all, after all the folks that are interested in wear aren't going to pick an OE tire, so why bother trying to market the tire line.
Don't believe me? Go to any tire manufacturer's web site and find the tires that are rated 600 or 700 for tread wear - any OE tires there?
Go look at the OE tires. Notice that these tires are different in name or in some other way from the mainstream tires. Sometimes the difference in name is something like a suffix - like "ST" or "AS" or "SL". This should be a signal that OE tires are somehow different.
I realize this may be difficult to comprehend, but the vehicle manufacturer dictate what tires they install, just like they dictate the shape of their headlights and the rims.
And each one has its own peculiarities. Tire manufacturers aren't happy about it, but the OEM's buy a lot of tires, their delivery requirements are fairly constant and predictable, and it's pretty nice to set up a production line to produce one size and deliver that to one location every day for 3 years.
The downside, is that the OEM's name isn't on the sidewall and the tire manufacturer usually gets the blame if there is a problem.
Anyway, I hope we've convinced you. The important thing here is that OE tires are different and you have to be careful when assessing their characteristics.