It should be of no surprise that filtration paper made to trap 1-2 micron size particles would be more expensive to manufacture than 5-6 or 10 microns, which can be found in less expensive air filters.
This... this right here. It rings a bell for me not because of anything automotive, but I think what does come to mind might explain some stuff anyway.
I live in the sticks. As part of living rural, among other things, I am my own water department. The well is 140' deep, and pumps a beautiful and constant 46gpm. Problem is, while it's perfectly potable as it is, the stuff has a lot of Iron Sulfide in it - harmless, but stinky, and leaves red iron stains all over everything.
So - I filter the water.
I have a wide variety in filter choices, but I'll save some time and cut ot the chase:
* The OEM filter (Pentek BB-20 Carbon) is 0.5 micron with a carbon filtration core, costs $60 each, and lasts 8-10 weeks on average.
* The cheaper $30 filter elements (usually made in China by folks like RonAqua and Tier1) range from 5-20 microns, and last only 2-4 weeks before the carbon is shot, the filter wears out, and the yucky sulfury scent returns to my faucets.
So what's the point? Well - you get what you pay for, yes, but going cheap is often more expensive in the end.
Now, back in the automotive world? Holy crap, y'all... unlike the overly-damp world of water filtration, OEM paper filters for the truck are often quite cheaper than the semi-exotic bullcr- err, I mean - products that they sell to allegedly increase performance (though a bit more than the cheapie paper stuff on the back shelf at the local WalMart/AutoZone/O'Reilly's).
Kind of a no-brainer here.