Why so many Yamaha's with new powerheads?

[mickt]

I want to start this thread with saying I'm not downing Yamaha outboards; I really like them and would put one on my boat in a second. It's just that since I have been looking for another used boat, it seems that more of them than any others have had the powerhead replaced, and some of them are not that old. So, I was just wondering, does Yamaha run a leaner mix of oil/gas? Could that be what causes them to need powerhead replacement sooner? Again, I'm not trying to start an argument about Yamaha outboards, it is just a trend that I have noticed.