I'll stay (mostly) out of the oil change interval argument other than to say there are so many variables, and not all of them can be explained.
We had a GM (General Manager) who used to get a new conversion van for a demo every 3 years at the dealership where I worked. He brought it in for oil changes at strict, routine 30- 40,000 mile intervals.

No joke. In just over 120,000 miles the history report showed 4 oil changes (he drove the crap out of his demos, fishing trips and what have you). And no, he never had oil changes done elsewhere. Never had an engine problem and did not use synthetics. Under the valve covers it was dark, but very little sludge. Why? I have no clue, but that's not the only case I've seen.
Then you have the other extreme:
http://toyotasludge.com/victims
I have personally seen many engines with very low miles on them do this. The ones we saw almost all had routine oil changes done at our dealership at the time so they received the same bulk oil brand as the Fords (Ford/Toyota dealership) which was Motorcraft (not sure who blended it at the time, may have been Ashland..).
Now, I'm not bashing Toyota, so don't go there: Toyota stood behind the vehicles in our dealerships case and fixed the problem, I'm just using this because I have first hand experience with these and to illustrate extreme cases. I've seen similar things both ways with many different manufacturers.
To sum it up though... why take the risk on something as simple as an oil change? Imagine what those engines that had problems would have looked like if they had 30,000 oil change intervals?
And I hope no one here ever bought a used, late model, high mileage Green E150 Universal Conversion van

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