Re: first text in bold - Massive exaggeration.
Re: Second bold text - not true. Windows Update drivers are from the respective manufacturers, example: AMD's SATA driver is from AMD, Nvidia's graphics driver is from Nvidia, etc.
However, I would modify this advice in the following way:
The drivers that ship with Windows are unlikely to be as good as the latest drivers from either the board manufacturer or the chipset manufacturer. In the case of LAN drivers, especially Realtek ones, the default drivers tend to have issues relating to sleep mode. In the case of audio drivers, Windows will install the default 'High Definition audio driver', which rarely works quite as well as say the Realtek HD audio driver. Occasionally I have used the default Windows driver as a fallback when the manufacturer's driver doesn't work as well, but that's pretty rare.
Personally, I would try the motherboard manufacturer's drivers first and if they're in some way unsatisfactory, then go for the chipset manufacturer's drivers.
I've seen issues caused by modifications to a motherboard manufacturer's implementation of (e.g.) audio which made it so that the motherboard manufacturer's drivers worked better than the audio chipset manufacturer's driver.
However, In the case of more popular mainstream stuff (like say an nvidia/AMD graphics driver) I would go straight to the respective chipset manufacturer first.
These days, the reason for a newer driver being made available on Windows Update is because an issue has been found in an older driver which is for some reason not considered a good driver to use (presumably for functionality/stability reasons). I've seen this umpteen times for wireless adapter drivers for example, and the WU driver not only worked but fixed an issue I was experiencing with the adapter (eg. authentication/encryption issues).
One thing I wouldn't ever do is replace a driver unless I had a good reason to (with the exception of drivers that come with the Windows installation). "If it ain't broke, don't fix it". Windows Update drivers had a rep for some time of breaking functionality, that's where I think G73S has their opinion from. However, it has been some time since I last saw this happen (and I've done a lot of driver updates this way).
With regard to driver improvements and WU, I posted this thread semi-recently:
http://forums.anandtech.com/showthread.php?t=2373354
Coming back to the OP topic, I have reasonable confidence that downloading drivers from the Realtek site should work fine. I would expect them to work better than Microsoft's standard HD audio driver.