Switching from a Microsoft intellisomething keyboard to a Model M (and a Logitech web keyboard before it) reduced my wrist pain (and I'm already on Dvorak). At work, I'm now using a Microsoft keyboard once more, and have noticed a marked increase in wrist pain.
I think the shallow travel on the other keyboards means when you smash the keys, you don't get as much resistance meaning you hit the base of the keyboard with more force, causing more pain.
Think of it like the old cars. People think they're incredible because they don't dent and are made of solid steel. In reality, you need the car to dent (all the way until it reaches the driver safety zone) in order to reduce the force of impact. The crumbling of the bumper consumes force that would have gone into the driver.
Same with the Model M. The buckling of the keys consumes that pressure rather than throwing back into your joints and your wrists. It's healthier that way.
I don't disbelieve you -- and, in fact, would report the same. Model Ms are awesome.
What makes a good keyboard is very much a personal thing. It depends on many factors. How tall you are; what position you sit in; what kind of chair you use; how high your chair is adjusted; what your posture is like within that chair; how high your desk is; how high your desk is relative to your chair; how the monitor is oriented; how long your arms are; the ambient temperature; how large your hands are; how strong your fingers are; what position you hold your fingers in over the keyboard (I maintain that holding your fingers over the home row as a default position is insane); how often you take breaks; what kind of exercises you do during those breaks, if any; what kind of exercises you do before sitting down to type, and when you're done for the day; and how many hours a day you type are the first few factors that spring to mind. I didn't have to try hard to come up with this list.
So the Model M works for you, and it works for me too. Lucky for us, because they truly are sweet keyboards (...till you try to hook one up to a mac). But that doesn't mean they'll work just as well for everyone else.
(The same goes for pointing devices, too.)
Random observations and anecdotes:
Unlike many people these days, I learned to type on - gasp - typewriters. Classes were on electrics although I often used a manual, too. I learned fairly early on that for long typing jobs, you have to learn good hand position and use the least force that will do the job.
The model M caused me problems but not wrist problems. It caused me problems in my fingers. After a few hours, that kick-back from each "click" adds up.
For some good pictures of good typing, look at old movies that feature professional secretarial pools. Keep an eye on the ladies' posture, hand position, and light touch.
These days I also type with a light touch partly to extend the life of a somewhat expensive keyboard - one that let's me type without rotating my wrists (e.g., the typing position is similar to shaking hands rather than to picking up a pencil).