On Fri, 2 Sep 2011 10:04:55 -0700 (PDT), ed_h
wrote:

That gap seems to have
closed these days, but perhaps there's a lot of inertia left in the
system - 3000mi changes used to be the norm in the US, so that's what's
still advised even though modern engines don't need it.

So you know better than the engineers who designed the engine?

At risk of harping:

The engineers that designed my engine say to follow the advice of
their oil monitoring system
The oil monitoring system on my car usually tells me to change at
7000-7500 miles.
I'm a typical driver whose driving includes some of the items on the
so-called "severe service" list

In effect, the engineers who designed my engine are telling me that,
for my driving, 7000-7500 miles is appropriate.
The manufacturers are, in effect, saying your car will last through
warranty with 7000 to 7500 mile oil change intervals. It will most
likely last as long as the average new car owner owns the vehicle.
They are not saying anything else.