I certainly didn't intend to flame anyone earlier. :o Running is a great exercise for those with no predisposition toward joint problems. It can be done in nearly every type of weather and away from traffic (hence the safety factor) and it doesn't require one to purchase an expensive bike (of course, neither does cycling). All a person needs is comfortable clothing and two decent pair of running shoes. I say two pair because the soles can compress during a run and may require more than 24 hours to bounce back. By alternating running shoes that isn't an issue.
That being said, running is not vastly superior to any other form of rigorous aerobic exercise that involves large muscle groups. Whether a person is running, cycling, rowing, stair climbing, shoveling snow, doing a combination of squat thrusts & jumping jacks, or extremely fast paced (circuit style) supersets while weightlifting, work is work. The only difference is how much work gets done with that activity. If you want cycling to produce the same results as running then stop dawdling and lollygagging and bump up your speed! Don't be a girly man! 😄 (Thanks Arnold!)
Trust me when I say that shoveling snow is an asskicker of a workout. Anyone that doesn't believe me can visit my mom during a nice Indiana snow storm where the drifts are a couple of feet deep and shovel her huge driveway. It's harder than any running I've ever done. However, unless you live in the Antartica, it's hard to do year 'round.
I remember seeing a study that showed walking up an incline will burn more calories and whip a person into shape faster than running on the flats (of course, that would require a nearby mountain or a treadmill with an incline feature).
Also, if one is using a Borg Scale (http://www.brianmac.demon.co.uk/borgscale.htm) to guage their effort level for running vs. cycling then their argument doesn't really hold any water. Perceptions are very misleading. How one feels about an exercise or activity may or may not accuratly reflect it's training value.
I would also like to debunk this one. I think I read someone state that the human body will lose weight faster while running because it somehow intrinsically knows it will be better off by dropping weight thus making it more efficient. Poppycock! Using that logic, then the converse would also hold true and a swimmer would store more bodyfat because their body would somehow know that the extra bodyfat would make them more buoyant. That's a good one! What the human body does know is how much work is achieved, whether it's running, cycling, rowing or shoveling my mom's driveway!