4% failure rate on mainly the old MMMs isnt too bad at all, especially given its power handling capabilities and built in switching BEC & easy to use pc programmability- compare that to cooked Schulzes that they (schulze) would refuse to warrenty 99% of time, or the expensive MGMs that are a nightmare to programme via pc, and it suddenly doesnt seem so bad.
Besides, no other company that I've seen has ever released failure rate info, and some even deny a problem with their escs and just fix the issue in silent- Castles openess should be applauded, rather than used as ammo to find some non-existant design flaw in their escs thats causing failures; even then the flaws are fixed with each new version of the esc, working towards making it truelly bullet & idiot proof.
As for the same user killing multiple escs, its like I said, often either a setup issue (same setup each time = dead esc each time), some kind of external problem (landing a big jump at the track without any padding under the esc, resulting in physical damage), or just occasionally, freakish bad luck
EDIT:
upto a 60% failure rate on xbox 360s has been reported according to numerous online poles and feeback from retailers, yet people still buy them happily knowing the odds are against them getting a working system for any length of time. 4% looks rather awesome by comparsion...