I, too, see that, and I understand and condone it. It's a comfort thing: if you're just beginning to bike, the very notion of hovering so far above the ground that you can't "save" yourself by quickly and firmly flattening both feet upon the pavement surely is intimidating enough to let you dismiss whatever may be said by a more seasoned bicyclist about "proper leg-extension."

Once a rider has become accustomed to balancing and to the very thought of being on a bike, I feel she or he should be encouraged to raise the seat such the legs extend more; a good mode of persuasion might be to ask whether the new cyclist feels fatigue or pain in his or her legs, after riding. Even at the final point, however, I don't buy that the angle that should be left at the knee is anyhow "universal," and this comes not only from the existence of different types of riding (for instance, the person may bike just ~a mile and a half every other weekend, and even that through some quiet suburban streets), but from that of different kinds of riders, with varied physiques, preferences, and areas of comfort.