Uhh... I was thinking devs (MK for KotN; can't remember who was the one mainly involved with SI, was it Kurt Khulmann?), but I think "both" could work as an answer to that.
MK and Tedders both wrote quite a bit for Oblivion, and Kurt Kuhlmann and Gary Noonan were employed through Daggerfall and Morrowind, respectively. If anything, SI was the game that didn't involve any outside help, and SI managed to contradict established lore so a freaking god could have five seconds of vernacular, dull exposition. "...my realm expanded across Oblivion through the centuries..."