Nope, even then, think of how much QA would go into something like this. They probably have 6-8 months of features that were built on this kernel. Upgrading the kernel before would mean needing to redo everything - all of the QA, UAT, months of prep work. Companies who hold up these big releases for us aren't like us just clicking perform upgrade, it's a massive process that needs signoffs and confirmations. That's why I say they probably just drew a line in the sand and said "We can't risk destabilizing it just to perform an upgrade" - or for all we know they did do the upgrade, realized it broke something critical, and decided against it.

We all know if they rolled out a broken release everyone would be on every forum with pitchforks calling Valve the devil. They weren't just being idiots by not upgrading.