Curious that the cabin filter isn't used all the time...

This isn't true. The filter button closes off the outdoor vents and raises the fan speed to concentrate the scrubbing but those of us who never use it can tell you that the filter accumulates much dirt over the months.

 

This button is to allow you to shut off the outside air for a short time if you are in a dusty area, smelly exhaust, etc. The air coming into the cockpit is always through the cabin filter. The recirculation on the heater only shuts off part of the outside air for safety reasons because of the possibility of exhaust leak into the car.

 

Hitting the scrubber button also turns on the A/C compressor to keep condensation down.

 

Our cabin filter was pretty dirty after only 15k miles.

So I'm convinced that it works.

It's hard to see in this pic, but the pleats were full of seeds and small bugs.

 

I think you're reading about the Micro Dust and Pollen Filter. That's an extra filtration system, I think with some sort of electrostatic charging? This is in addition to the regular filter, which is in the air flow all the time.

 

The best explanation of the cabin air filter, the Dust/Pollen button and the outside air vent door control that I have read goes like this:

Even in the Recirc Mode the outside air vent door does not close completely in order to allow a small amount of fresh air to flow in the cabin for personnel comfort and to prevent fogging of windows. When the Dust/Pollen filter button is pressed the outside air vent door is closed tightly in order to circulate only inside cabin air through the air filter to remove dust and pollen from inside the cabin. During this time the AC is used to defrost the windshield to prevent fogging. The Dust/Pollen filter has a 3 minute timer to prevent the system being left in this mode and not allowing fresh air to return to the cabin.

 

No, the electrostatic filter is installed in the 4 and 5 level cars' driver's face level vent and is called PlasmaCluster. It causes dirt to stick to the vent surfaces, requiring no separate filter to clean.