Well, the shop shouldn't be abligated to honor the warranty. For that, you will need to go to PIAA directly. That's what 3 different shops suggested I do, and when I finally got off my ass and called them, they sent me a set of bulbs just like I explained in my post that I linked. So, if the guy who owns the shop you went to doesn't honor their warranty, it's because he doesn't have to.
About the bulbs burning out because of the higher wattage, that isn't entirely true. The PIAA's I ran that burned out were 12v 55-60watt Superwhites which are fine. As a matter of fact, most of the bulbs that PIAA sells are 12v 55-60watt that perform like 110-135watt in some cases. The rep at PIAA even acknowledged that there was a problem with bulbs I purchased that burned out. You are correct about people buying the higher 80-90watt bulbs and when I was looking at those, the sales guys at the shop were telling me that those will probably melt the inner housing of my fog lamps or headlamps. Then they recommended the PIAA Xtremes, which I though were way too expensive at $79. Thank god PIAA gave me some for free through their warranty.