I can't speak for that poster, but I have played Morrowind and Oblivion, and I can attest that there were many things that have been added over the years. Oblivion added Radiant AI and various NPC factions, giving NPC's schedules and giving enemies more interesting behavior (such as bandits, marauders, and undead battling one another, whereas in Morrowind this only happened if specifically scripted), and it added the concept of perks to the TES series. Skyrim improved on this, giving us creatures and NPCs that gave warnings if you got two close before turning hostile (not unlike the system in Gothic 3), bandits fighting over dropped gems, archers deliberately moving to avoid getting hit by ranged attacks, mages that switch their spells to adapt to their foe, wolves flanking their prey, vampires turning invisible and running when they decide they're outmatched, not to mention improved NPC banter, with unique conversations between specific NPCs.