The other thing is that more airflow doesn't necessarily equate to a usable power increase. That or it's a minescule increase for the money spent. More air at 5K rpm might deliver a few ponies but how often are you at 5K rpm? Plus, in many cases, unless there is some additional tuning done to the engine, you can't realize the benefits. I base my comments on having participated in lots of dyno testing of various products.
If a vehicle is used on the street in a relatively clean environment (not the dusty desert cities, for example) a few percentage less in filtration capability is almost a non-issue for many people. But on the other hand, for some, me included, who live in a fairly dirty environment, I need every pore in the filter working for me and oiled cotton gauze filters won't cut it for me.
That said, I am tracing down a comment from a reliable source that says some cotton gauze filter mfrs have increased the density of their filters for better filtration. Wonder if that's true?