The fault in your reasoning is the increase in AMD marketshare. How did it grow to almost 30% in less then 18 months? Someone must be buying them, and someone must be selling them. Not everyone sells them (Dell for instance), but enough have confidence in the product to have made such a dent in Intels marketshare.
Replacement chips for fried Athlons do not increase marketshare. They come from a small percentage of users who will try to overclock, who remove and replace the HSF on a weekly basis, while not really knowing what they are doing.
My Tbird is 10 months old, and runs 18 hrs a day 7 days a week. It has NEVER locked up. Never as in not once. I have never removed the HSF, and don't intend to (unless I decide to put in a 1.3ghz processor for under $100, in another month perhaps under $80).
But you are right that the AMD chips are fragile. They should have a stronger package (core) and should have effective thermal protection. However, if left alone after installation, they will run trouble free.
<font color=blue>This is a Forum, not a playground. Treat it with Respect.</font color=blue>