WHERE? If it takes you three blows instead of one to kill every rat and bandit you meet its not "more difficult" its just boring. And if thats not so then your levelling is false or your armor and weapon are not "up to date", sorry.
Oblivion is more difficult at higher levels. Haven't you ever fought a goblin in Oblivion at level 40 before? My equipment is always up to date, and I level well, but creatures level with me, and goblins are a nightmare at high levels. Since the average goblin is still powerful when I'm at level 40 and it can actually kill my character, Oblivion is more difficult than Morrowind at higher levels. The player can easily become powerful in Morrowind. Why wouldn't Oblivion be more difficult with more powerful enemies? I like being able to become powerful in Morrowind. It's easier in Morrowind than it is in Oblivion. Morrowind reallly isn't that hard, and there is nothing to fear at higher levels. It's easier to do many things in Morrowind.