They're also using an unpublished variant of the chosen-prefix attack, which presumably is what allows them to win the weekend race to generate a collision with a predicted timestamp/serial pair.

We're also focusing on the algorithm, but not really accounting for the fact that simply owning a cluster of PS3s doesn't give you the optimized math code that generates the birthday bits during the weekend window. That code is itself presumably harder to write than any zero-day exploit.