I'll have to disagree here ^^
Facing a Bear, Troll, Vampire, Tiger or even that Restless Draugr in Bleak Falls Barrow simply results in death on the lower levels, if you actually decide to fight them and not run away completely.
It's not like you can run to them, hit, run away, heal and come back for another hit... they aren't that slow so that you could abuse this.
Trolls even start healing themselves.
Higher difficulties actually make you have to pick fights. They make you use things like Conjuration and the stones in the landscape to distract your enemies.
Survival becomes way harder in general.
You start picking the fights that you can make it through and actually avoid fights to a higher level.
Going alone against 3-4 bandits won't turn out too well either.
I don't think Bethesda's difficulty system isn't too great either.
But claiming that higher difficulties aren't more difficult is simply wrong.
The fights aren't taking longer... they are just way more lethal, if you take damage.