Risk management. You have to at least acknowledge the fact that you have a percentage of failure in any given amount of vehicles. While your chance of having a failure is, thankfully, low, you still have to account for it in your decision making. This is why you buy insurance for accidents, though your chances are relatively low of having a major accident on any given day, you still have to account for the possibility. A warranty is nothing but insurance in the case of failure.
Like you said MOST vehicles make it just fine when they're properly maintained and modified, but there's always that chance. Whether or not you're willing to accept the risk is up to you.
Now, a reminder to you all about your warranty, if you modify your vehicle and something goes wrong, and you attempt to hide those modifications in the hopes that you will recieve warranty repairs, you are committing a form of fraud. The dealership is under no obligation to uphold their end of the deal when you are attempting to defraud them of the labor and parts required to fix what you screwed up. If you decide to be sketchy and dishonest, I would advise none of you to post about it on public forums at the very least. That is, if you are able to live with a decision like that.