Ok, I understand that and I am assuming you have sat in the Aeron for more than a few minutes. Most office seating manufacturers offer very reasonable warranty periods as a standard practice.
I have 15 years in the furniture industry and my specialty is office seating. I have no financial gain by your choice regardless of what it is, I just think that the Aeron chair is far over priced for what you are really getting. It's your $$$ so I don't really care how you spend it. You aren't buying a warranty you are buying a chair. Your body will change in the next 12 years and the chair will not quite 'fit' you in that time. Buy what fits you now. What delivers the best comfort and what fits your budget. The offerings I mentioned are competing products, no different than motorcycle brands. You can get two of each of the ones I mentioned for the same money.
Other than the fact that the Aeron is cool looking what do you like about it? What do you dislike about it?