there needs to be a distinction from normal gameplay (which is what they are referring to) and completionist playstyle where absolutely everthing is looted and/or picked and sold or stored somewhere. most people dont do the completionist route and had it not been for mods like OOO it would have been pointless for oblivon anyways since their dungeons are all the same and the loot is levelled.
It would be interesting to see what the average playthrough length is, but from participating in many discussions on this forum, I get the sense that at least among forum members there are a lot more playthroughs of Oblivion and Morrowind in the 200 - 500 hour range, than the speedy playthroughs like yours in the 20- 30 hour range.
In my view if you finish the game that quickly you are missing out on 80% of the game. TES games are not like Bioshock, Mass Effect, etc., where it's a race to the finish. Those games last 20 - 30 hours or so, but Oblivion and Morrowind are truly massive games. I'm on my third playthrough of Oblivion and I'm still discovering all kinds of new stuff. I have never even completed the Thieves' Guild questline, the Fighter's Guild questline, the Knights of the Nine or Shivering Isles yet (obviously not the main quest either).
The "completionist" playthroughs you mention are more in the 1000 hour + range - those are playthroughs where people are actually visiting every dungeon in the game, etc.