I have to agree, this has been long overdue. Windows Update has been slowly rolling out a similar system, providing drivers to common hardware, but they never stay up to date, which is critical with GPU's. I tried the Steam update myself, but due to my aged 3650 AGP card, it simply redirected me to the AMD driver page where i had to manually enter driver details such as type, model and OS, so there are still kinks in the system. Many of the so called Driver update managers that float around are nothing short of cons to be honest, either charging people for a little tool that tells them a new update is available (they still need to go to the website and manually select all the details themselves), or are adware infested gimmicks. Even the software managers of various flavours across linux can't catch all the drivers, but are a darn site better than what's available with Windows.
In all honesty, it would be nice to have some kind of software manager for windows which handled drivers as well, but it'll probably end up like like a heavily filtered app store like Apple. It's unlikely to happen though, purely because of the shear volume of applications, i mean, there are 100's of different applications for every single task conceivable.
This is still a very important step though, and Nvidia needs to get on board, Intel too because many users still have Intel IGP's in Laptops and such. There's more to Steam than 3D behemoths requiring multi-GPU systems. Speaking of Multi-GPU, SLI and Crossfire config updates through Steam would be nice as well (since they are separate from the main driver).