I disagree. Codec packs from Shark007 undergo extensive testing, and I have yet to find fault with them.
I can play all formats using native Windows programs (both WiMP and WMC) and the codecs are there performing the same functions as the built in codecs that Micro$oft ships with Windows - there are just more of them in this case.
Why buy an ATV when you already have a golf cart for traversing the greens?
Using a third party player is great - until you decide you want to expand upon what you do (like using extenders in WMC) and all of a sudden realize that you can't - b/c KMplayer will play videos that WMC won't. Then you realize that you want to use the Media Center remote - only to realize that it only handles basic operations like forward, rewind, etc, and you still need to power on WMC to watch Live TV....
1 product - WMC - handles it all for me, with the exception of BD, b/c I don't have a BD player right now, and thus have no PowerDVD.
I used to be the same way about codec packs - every one I had tried had hosed Vista left and right - until Shark started making his packs more freely available. After that, I never looked back.