Part of the problem here is that there's been SIX composers for this game (seven if you count IS's dad), and everyone tends to make music differently. Different programs, different styles, different resources, etc.
As far as the Oggs are concerned, AJ generally takes modified versions of the MIDIs specifically created for the purpose of upgrading, and running them through his Korg synthesizer before recording. Cyan didn't do it this way when he made the current Oggs of Stuf's Techno Hill tracks though, once again showing how everybody does things differently.