I applaud those folks for running that filter test. It shows a possible why the manufacturers choose to continue using paper filters instead of switching to oiled filters. Well that and the fact that most users will not clean a filter... To play devils advocate I went looking for the best article arguing for an aftermarket air intake:
Dyno Test: 4 K&N vs. AEM 5th Gen Camaro Intake Options - LSXTV
You can see the affect of heat soak on the intake with the large aluminum pipe.
The camaro in question has exhaust manifolds that can support 500+ hp, and it seems to have a smaller stock air filter and a intake tube and as a result there were some impressive performance gains on the dyno using these perfectly clean filters. Even with this ideal setup please note the RPMs where the numbers start to pick up. You don't see the toted improvement until the engine exceeds 5000 RPMs, a level that most RVs will never see unless they are running the Chevy 6.0L. There is some improvement down around 3000 and 4000 RPM but not enough to feel the difference. On our rigs that are limited by the restrictive exhaust manifolds I question whether or not the observed improvement would be this dramatic. You can only move as much air as the pump allows and when you have a restrictive exhaust that will also limit the amount of air the engine can pull in. All of these things are connected so changing just one item will often not have as big of an affect as expected thanks to a bottleneck somewhere else in the pipe. To take full advantage of a performance intake you would want to swap the exhaust manifolds for headers and remap the computer to take advantage of the improved volumetric efficiency. Then you will see a marked improvement. However you will also see a pretty good dent in your wallet as well. This is the approach that Banks takes with its power pack and that bad boy will set you back 2000+!