I think the guy was a JD salesman and he was trying to get people to come trade in their machinery while it was still running. /forums/images/graemlins/laugh.gif
If you figure the typical tractor engine is run at fairly high rpm while it's working, you could equate it roughly to a car engine running at freeway speeds. Thinking like that, each hour is about the same as 50 to 75 miles on a car or truck. Semi's last well over 500,000 miles, and 200,000 on a gas engine car or truck is not uncommon -- I do it all the time.
I had the gas engine in a 1972 Cadet finally die 2 years ago after being overhauled once. That tractor mowed lawn, pushed snow, mowed fence lines, and made trails in the woods for me. It also hauled brush and a trailer full of rocks that weighed more that it did while I was building a stone wall about 75 feet long and 6 feet high. (Boy, an FEL sure would have been nice for that job!) I'd estimate I put over 250 hours a year on it, but have no real way of knowing. I put a new 12 hp engine in it to replace the frozen up 10 hp and still use it.
The new lawn "tractors" that are built to a price point will not last that long. The Cadet guy at my tractor dealership figures the typical $1000 mower/tractor with a name brand is good for about 4 or 5 years before it needs repairs that are sufficiently costly to make the owner opt for a new machine instead. The work on my old Cadet, which involved a new driveshaft and some other stuff, came to about $1800, which at first seems nuts. On the other hand, it'll probably last another 30 years being used the way I've used it. I don't think a $1000 mower would last 1 year under those conditions, if it could even do some of the work.
I don't know how many hours are on my little 16hp Kubota. The hour meter was disconnected at 1500 when I bought it. It was made in the late '70s, was used for barn cleaning and other less than glorious tasks. I've had it for about 4 years now and work it pretty hard. It starts in single digit weather with no major difficulty, bush hogs, plows snow, cleans the barn, hauls manure, hauls firewood, hauls logs, hauled a trailerload of lumber that my Dakota couldn't bring up the hill, moves dirt, rips out multiflora, and generally does everything I ask of it. All I do is fuel it and change the oil and filters a couple of times a year. Oh yeah, it gets a bath about once a year whether it needs it or not.