I'm reading
a book right now about setting prices and going through price negotiations, and the theories promoted in that book are being used in this situation where they are estimating oil flow from this leak. BP and others aren't trying to agree on a price like you would with a sale, but they are trying to arrive at a number. One of the main points of the book is the idea of an "anchor" number. Once one party sets an anchor, all number floated after that anchor tend to be pulled toward that anchor number.
BP threw a number out there early on that was very low. They won the race to set the anchor point. So now everyone who has seen or heard that number, whether they realize it or not, is thinking about that original (low) BP number. Any future numbers are going to be compared to the low number and even if they are actually accurate they will be viewed as being unreasonably high. The burden of proof will be on the new numbers coming out to prove that they aren't unreasonable.