While "other engineers" take the time to understand how theoretical life relates to REAL life....You make this sound like a few slips of the clutch will ruin it. You couldn't be farther from the truth. That is where REAL WORLD EXPERIENCE with an actual slip clutch on an actual tiller being used in tough conditions, and while we're at it, for a great many more hours (at one time) than most tillers see in a lifetime of "average joe" use. Don't you think we've advanced enough in technology by year 2011 where we can design and build a slip clutch that ISN'T a fragile, single use only, "weak link" rather than the dependable, built in FUNCTIONAL protection it SHOULD be? Maybe you're a real cracker jack operator and NEVER put ANY stress on ANY part of your equipment. Who's to say you aren't.....But, most folks using slip clutch equipped tillers aren't going to run along in the dust behind the tiller and continuously monitor the temperature of the gearbox.....This stuff gets used in REAL WORLD use...So the likelyhood of the slip clutch getting a bit of abuse is a given....So any engineer worth his salt would spec a slip clutch that CAN slip, WILL slip, and SHOULD slip, and at a point far enough ahead of "catastrophic failure" to protect the tiller without taking things to the very limit.
Long story short, there are no points to be gained by using a tiller for it's entire life without the clutch ever slipping for a couple or three seconds at a time. There's enough evidence that won't do long term damage with the OCCASIONAL "slip". You can do the lab test's under controlled conditions.....You can ride on the tiller to monitor the clutch and gearbox as you suggested.....
I'll stick with what WORKS, which is a slip clutch that actually does something rather than collecting dust in a barn.....