To be fair, on the Rivendell site, Petersen doesn't totally disagree that some riders pull up. He admits that experienced racers do. He also, I don't believe, discusses fixed gear riders.

What he does say, and is probably right about, is that many inexperienced riders are convinced by salespeople to buy clipless pedals with the idea that they will automatically improve their efficiency. That is obviously not always the case. Petersen also cites a study, I believe, where clipless riders were shown to have less weight on the pedal coming around, but not actually pulling up. Again, this applies to average riders.

Rivendell caters to bicycling enthusiasts who commute, tour or just go for leisurely rides in the country. Racers are not their thing.