I don't find that strange at all.

I'm assuming that it wasn't the plug going bad as much as buildup on the electrode. It's rather common on averagly maintained vehicles and some models. Also, if a bad batch of gas was gotten it could of multiplied this problem greatly.

I remember when I did the headgasket on a 1998 Ford 3.8L V6, I had to replace all of the plugs because one of them had the electrodes completely clogged and 4 others had substantial buildup.

It is an exponential effect, once the plug starts to lose spark, the burn becomes less efficient, and the buildup increases.


Now I could be wrong and buildup might not have been the issue at all. But from the limited ammount of information that was given, I'm going with that.