Guess I should have said "typical spring failure is do to fatigue from compression and decompression in properly designed springs."
You are correct, there are other ways to ruin springs. But a magazine that is designed properly should have excess compressive capacity built into the spring, a safety factor if you will, that should exceed normal compressive loading expectations.
It is an interesting topic indeed. Gotta love physics
http://www.spring-makers-resource.ne...les/fig_37.pdf
If you notice, these losses occurred at temperatures over 200 degrees F at over 100 hours. Extreme events and conditions will make any metal behave differently than at room temperature.
Article outlining the various materials used in magazine springs:
http://www.whitesounddefense.com/pag...Materials.html