In years past, the PC maker might want to stay in the device-driver loop for quality control reasons; drivers were often so bad that they would totally blue-screen the system when used with popular games and applications. In that scenario the PC maker was the last line of defense for the customer, and of course it kept their support costs down to avoid shipping garbage for drivers.
Things have changed in the past few years. Microsoft has created extensive test suites that the driver must pass before it is certified, and certification is required to get a Windows logo and have the Windows Hardware Quality Labs (WHQL) sign the driver. Most PC makers require their component suppliers to provide a signed driver. This process has made drivers much less problematic than they have been in the past.
One of the few reasons that PC makers have to stay in the loop relates to their marketing focus. Some PC makers love to ship their PCs with software utilities that supposedly add value, but most important (to them), stay in your view with various icons for branding. Conversely, the PC makers often don't want the component maker's branding on the driver, even though the component maker wrote the driver.
Still, bugs do arise; security problems crop up as well. In those cases, users want to be able to get new drivers as quickly as possible. Those fixes are going to come from the chipset and component makers, but they often still pass through the PC maker. Nvidia's move here is intended to eliminate that middleman and get new drivers to users faster. I'm glad they have been able to get the PC makers out of the way.