I am doing closer to 85% highway miles these days.Don't you do like delivery driving or something? I'd be curious to see what your average speed is (and how many engine hours you have). A Crown Vic getting pounded as a cruiser or a cab in NYC for 10 years to get to 200,000 miles is considerably different in terms of wear & tear than an owner/operator courier or delivery vehicle that's putting on 100,000 miles per year.
@Shannow's point was, and is, that as long as the vehicle makes it to the scrap heap by some other means, then the oil did its job. If the has more wear than an engine that was run on a heavier oil, does that really matter at that point? The thinner oil saved the owner some fuel and the manufacturer some emissions or economy credits.
We've seen posts about Toyota engines burning oil, people blaming the low tension rings, or the long intervals. Viscosity choice is another piece of that puzzle. I'm sure in the majority of situations, all three of those things work fine together and the RAV-4 makes it to the wreckers because Jimmy hits a tree or the trans drops out of it, or some uninsured yahoo plows into it at 150,000 miles and it's a goner.
BUT, none of that changes the validity of what Shannow posted.
Typical speed on the highway is 75 mph.
Much thanks to OVERKILL and Shannon for all the info on BITOG.