A few comments I've seen indicate the the Macbook fan profile is very conservative, such that fans are only spinning at moderate speeds even as the CPU is overheating and aggressively downclocking. If they're claiming to fix this using software, it seems that adjusting the default fan profile is one of the only things they can do. No idea how this relates to the mentioned "digital key" though.
My take on the "digital key" part is that OSX probably requires each system component (software/driver) to be digitally signed. If a component's validity and authenticity can't be verified, the OS will just refuse to use it.
Having a component of thermal management disabled could make the software side inoperational, leading to hardware-imposed throttling once the temperatures climb too high. This hypothesis is also compatible with the fact that the fans don't ramp up even when throttling: the software that should instruct them to do so isn't working.
I'm not sure of how a software update can make the cooling more efficient... The heatspreader/heatpipes are undersized, that's it. it is a conceptual issue, hardware issue.
Even if they make the fan much faster, I doubt that it's enough to cool a 3.8 ghz turbo mode without make it throttling.
If Apple wants people to believe that they can fix something like thermal (or vrm?) throttling in software, then they better be prepared to offer a real explanation instead of trying to breeze past it with Star Trek technobabble.
Looks like the update did bring some improvement. It looks like previously the CPU would aggressively try to hit max turbo clocks (4.3 GHz for all core), overheat, throttle back (sometimes well below even base clock), cool down a bit, and then repeat. So the frequency was bouncing all over the place. With the update it seems to more intelligently target a boost clock that's more or less sustainable (~4.0 GHz). It seems like this improved overall performance, in addition to making it more consistent.
Maybe the "digital key" is like the keychain password you have in Mac OS that no one understands the purpose of. You have a login password, you have a keychain password. You reset your keychain, it never asks for it again except randomly when it prompts and you again have to reset it.