Do I still need to download and install something like K-Lite with Windows 8, or have they bundled codecs in to play the myriad of media types on the web? (.mkv, xvid, h264, etc.)
The best overview to this question is http://blogs.msdn.com/b/b8/archive/2012/06/08/building-a-rich-and-extensible-media-platform.aspx:
"Formats popular among the enthusiast community or with specific developers such as FLAC, MKV, and OGG, can have their own CODECs packaged as part of a Metro style app, since the Windows 8 media platform is highly extensible."
So, to play "everything" you still have to install individual codecs or packs.