The way that I look at ISO is as a quest for perfection. In spa world there are very few companies that are ISO so you could agree that it is not something that a company MUST do in order to compete. Those few who have done this want to stand out from the competition. They want to be the best possible.
With this type of thinking why would they sabotoge themselves by writing inferior rules and not reaching to be better. They could have saved themselves the trouble and expensive by just doing what the rest of the industry does.
As far as warranty goes. Warranty refers to manufacturers defects. It doesn't mean that there will be no expenses relating to maintainance during a warranty period. Many of the issues relating to warranty are due to 1) customer's unrealistic expectations or 2) dealer related problems.
For example, if the dealer has gone out of business or will not service the product for some reason, that is a problem. It is not, however, the fault of the manufacturer. Yet, no one gets on line and says dealer "joe blow's spa store" stinks. They say, X spa stinks. Meanwhile we have dealer who change brands every year or two and won't service the old brands.
Another thing that people don't always know is that manufacturers purchase pieces/parts from other suppliers. If something is warrantied or not may be up to that supplier not the manufacturer.
I have had customers whose tubs have frozen, whose water is green with frogs (really happened), who have issues with how they have taken care of the spa, that are surprized that their problem isn't covered under warranty.
Lastly you have the people who have done everything they are supposed to do and something just goes wrong. Those are the ones that a dealer will go to bat for. We will work with the company and the customer to find a solution. We will work at a reduced rate, we will help anyway we can. Sometimes it just isn't a warranty problem and it's no one's fault. With respect to each other and with the knowledge that everyone is working toward a solution and cooperation, it can get resolved.