Hi T-Keith,
Most of these particles are a lot bigger than 10 microns and are easily filtered. To get maximum life it helps to get the small ones out too. I myself don't want this garbage in my oil but unless someone pre-fills the filter then the big chunks will be caught the first time. By pre-filling you are actually bypassing the filter and putting the junk right into the engine.
I've never been a big fan of total solids and don't have much experience with this test so I don't have a good answer. I would expect these particles to show up if the test is done correctly. There are however a lot better methods of measuring solids.
You are absolutely right about this being outside contamination, unfortunately the oil is contaminated before it gets to the end user. Take a look at the reports I posted, they represent about 10 or more different brands of oil, several of which came from quart containers. Most of these are 15W40 diesel engine oils but I have tried to include a few reports of gas engine oils too.
When I am talking about several passes that is to get to ISO 16/13. Several studies show that a reduction of one ISO class will increase bearing life (ball/roller) by 5 times or more. We work with heavy equipment and have transmissions that cost $100,000, but the same principals apply to small gas and diesel engines and auto transmissions. Keep it cool and clean and it will last a long time.
Stinky
Next time you send in a sample of new oil ask for a particle count and patch test.