According to Jeff Jones, the director of Microsoft's security group, the Pwn2Own contest is "simplifying security to the point of uselessness."
Pretty much as useless as counting "vulnerabilities" without looking at their practical application, I'd say.
Note that all of the browsers at these events were eventually hacked, and all with pre-developed exploits. That fact that Miller was quicker than his competitors has little to do with the overall system security.
Actually safari gave up read and WRITE access to the system. Where as IE8 only gave up read access. Now both are very serious issues but WRITE access is way worse. So even though everyone knew this contest was approaching best they could do against IE8 was read access.