I wouldn't go that far. I can take a drag car and make make a good 8-10 nitrous passes and it be due for a rebuild, this same with atvs. I have heard of shees from 1989 that still run around without a rebuild (given slow). Longevity of a engine is a function of the driver. I can pound any four stroke into need of rebuild in a good year just as a 2 stroke. As far as cost, you can rebuild the top end 2-3 times on what it takes to go through the entire four stroke once. Sure, when you get a two stroke, you pay for what you get, high revs, high power. The cost, maintanence. Would you pay a small fee knowing that your quad was the best onthe track before you got there?
2-stroke KX500 3600$
2-stroke shees 4000$
Tossing mud on 4-strokes as I pass.......Priceless