Might have changed since 2011? I believe it was 91 days back in the early 2000's. Then for quite a while they tended to not stamp your passport, they just stamped your I-94. Now that the I-94 is out of the picture, they're back to stamping your passport. I've seen 4 passports with 2013 stamps, from different US entry points, and all had 90 days (not 91). Make that 5 with Ian's.
OP, please see the other thread for suggestions. Specifically, in your situation, I'd do the following: If flight arrives close to midnight, wait until after midnight to go through immigration. If you want to break your US journey to go to Costa Rica, Colombia, etc for a week, that would solve your problem. Otherwise, just pay the fee to have your ticket changed. If you can change your ticket after you've flown into the US, you could wait until your passport is stamped and you've had a chance to talk to the CBP officer to decide what to do. In such case, I'd suggest that you book a refundable return ticket for < 90 days in the future (so you don't risk being ineligible for the VW), then ask the CBP officer whether you would be allowed to stay 91 days or not... show him your old stamps that apparently allowed you 91 days. Post back here what happens :)
Regardless of what you do, make sure you have an outbound ticket within 90 days when you board your US-bound flight in Europe since there is a small risk you will be denied boarding otherwise. You can book a refundable ticket that you later cancel.