Unfortunately, these studies you quote are  5-10 years old (except for the
last link), and I would not put too much faith in the them anymore for
picking a specific product. The last study (see link above) gives the
following recommendations:

Oil filter Recommendations for the Honda Prelude (should apply to other
vehicles also, but the author only looked at filters available for this
vehicle):

1. "The Mobil 1 oil filter is well constructed and a decent filter.
Unfortunately, I'm not been able to get my hands on a stock spec'ed Mobil 1
filter (but have taken apart a few oversized ones). However, I have been
able to discern that it's made on the same line as the K&N filter, but will
a media that is slightly better at filtration. Based on testing by others I
still think this is a really good filter.

2. The AMSOIL SDF-20 filter is well constructed and lab tests show that it's
an excellent filter. At 6350 miles this filter was able to generate the
above lab test report and show that 10w40 oil in an H22A4 causes no
problems. On the other hand, it's big brother the SDF-44 did not filter oil
well at 13,000 miles. Proving that an oversized filter is not always a good
thing when it comes to filtration.

3. The K&N HP-1004 is a great filter. The internal construction is the same
as the Mobil 1 filter, but it does not filter the down to as small a
particle size. This filter is meant to maintain higher flow while still
actively filtering, as opposed to by-passing. Lab tests using Mobil 1 at
7500 miles indicates that this filter works as well as the AMSOIL SDF-20.

4. The FRAM x2 (and only the FRAM x2 Series) is probably the most heavily
constructed filter I've seen so far. Though all of the Japanese made filters
were of exceptional quality, the Fram x2 was as good in every way. Of note
with the construction were the following features: metal screen backing the
media, heavy metal end caps (all other Fram filters have cardboard), and 2
layer filter medium. Lab testing indicates this filter is fine at 5000 miles
use with Mobil 1. As with all of the Fram filters and OEM Honda oil filters
the x2 uses the standard spring loaded plastic by-pass valve that many
people do not like. However, lab tests do not indicate that the valve jams
or fails to work. It's possible that a hard enough impact at a sharp angle
while the filter was by-passing might cause it to jam open, but I suspect
the fluid within the filter would prevent this."

Is it likely that Toyota would try to save a few cents/unit on oil
filter quality when weighing that against the potential cost of having
engines fail?

I doubt it

Ron

Every time Consumer Reports has rated Toyota filters, they have said
Toyota Owners have it made. They are the best filters you can get. So, I
don't know what report you read (yet...I'll look later) but take a look at
the display in a Toyota parts dept. They look good to me...

These are interesting links. Toyota engines are more family oriented
than racing oriented so there is less discussion on it. People should
do more filter studies.

Purolator does make some of toyota's filters but the bulk comes from
south Asia. The cost is low and probably explains the inferior
filtration rating. I use Purolator PureOne with a multipass efficiency
of 98% (www.pureoil.com). The only other filter with a better
efficiency rating AND flow rate are Champion Lab filters (marketed
under GM AC-Delco Gold, Platinum or something like that). Other filters
I have not seen any writing about being better than PureOne.

If you can get a Toyota filter made by Purolator it's ok, then you
might as well get a PureOne.

I'm pretty sure those "studies" were done by an Amsoil connected
person.

I use Toyota filters on my Toyota, because they're $3 at my local
dealer, including a plug gasket.  On my other vehicles, I use
Purolator filters that cost $7-8.  The Toyota filters are built as
good or better than the retail store brands, and even come with the
gasket pre-lubed and the filter opening shinkwrapped against dust
contamination.

I have no doubt that the Toyota filters have sufficient quality filter
media, as Toyota would have to eat a lot of problems on
dealer-serviced cars.

FWIW, my local Subaru and Jeep dealerships use aftermarket filters
(Wix and NAPA(WIX)) on in-house oil changes.

Amsoil has some good products, but the multi-level marketing business
model puts many hands in the end user's pocket before the product is
sold.