I installed K&N's on my Roadster just yesterday, and noticed immediately the quality of construction.
Holding the pleats apart mechanically seems a no-brainer to me. The Mann filters (OEM) had more surface area to offer for filtration, but they would need it considering the number of compressed/collapsed pleats. I would wager that under high flow/pressure this would be exacerbated since the unrestrained "peaks" of the pleats face the airflow and not the "troughs". Any other engineers out there?