I've got to wonder how you know this for a fact. I've had two steel bikes break on me and my main bike now is an aluminum one with at least three times the mileage that either of the steel bikes had at the time that they broke. BTW, I also find the aluminum bike to be a little more comfortable on long rides than any of my steel bikes if they're all equipped with the same seat and tires (but at the moment the steel tourer is better due to wider tires and more comfortable seat). I find the comfort to be more a function of the frame geometry and fit as well as tire, seat, and bar choice rather than having much to do with the frame material.