zuluclayman

Matroska (MKV is the video file format of this) is an open source container format that allows multiple streams of data - it is often used for DVD rips
Ogg media (OGM is the video file format of this) was developed as a multi stream container format that was used as an alternative to other container formats in conjunction with a number of audio codecs (Vorbis etc) that were being developed a few years back - Matroska sort of developed out of Ogg.
There is no real reason I can see for either format to be used over others available as some media players won't play them.