As I understand it, the biggest mining pools essentially determine which client to follow, and we trust them to always do what makes the most financial sense to them.
Not true.
On March 12th BTC Guild had many blocks mined using the v0.8 client. Abandoning v0.8 meant a direct hit to their profits as a result of solved blocks that they'ld no longer receive the mined coins for.
What made BTC Guild switch to mining on the pre-v0.8 side of the fork?
The response to one question ... "What side is Mt. Gox using?"
Mt. Gox recognizing mined coins on the pre-v0.8 side meant those coins would have value and the v0.8 ones would not. So BTC Guild honored the will of the economic majority.
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http://en.bitcoin.it/wiki/Economic_majorityNow Mt. Gox doesn't automatically represent the economic majority, but in this specific instance hardly any of Mt. Gox's customers would give a care which action Mt. Gox took regarding this hard fork, so Mt. Gox essentially had sufficient representation that there didn't need to be any temperature taking to see where the economic majority stood, ... it was known immediately that v0.7 was the side of the fork that the economic majority sided with.