Yes, actually... you can sharpen a knife blade using circles instead of long strokes. Many people that sharpen freehand use a circular motion. It's one of the techniques that Buck used to recommend for sharpening their knives. They may still favor it. I haven't checked their web site or bought a Buck in some time so I can't say for sure. You can sharpen a blade to a certain degree with rocks... if you know what you're doing and if you use the right rocks. But you can also harm an edge with the wrong technique or rocks. Bottom line is that there are far more effective sharpening tools than rocks and they're still easily affordable and portable. The Spyderco Doublestuff stone that I travel with is thinner and lighter than the rocks he's hauling around and I would bet that it's a more effective sharpener for knife blades.
Axes and machetes, however, may be another story...
"If there are no dogs in Heaven, then when I die I want to go where they went." - Will Rogers 1879-1935