Apparently, K&N (for example) uses a nominal rating which they place at 10 um, while their ABSOLUTE rating is 40 um. Huge difference. They clearly advertize the nominal because it appears better than what is absolute. While FRAM and WIX ratings are absolute numbers.
Also the FRAM end caps aren't cardboard: they are the same cellulose material that the filter media is made from and it is woven right into the media, making it much less likely to come apart and tear off unlike metal end caps which are simply glued on.