There's more differences than just the legs between Morrowind's Khajiit and Oblivion's...
However, they are not major differences that couldn't be accounted for just by Bethesda changing the designs between the games a bit. Though, I could see them being the non-raht variety of Suthay, they're still stealthy types, and they still look like generic cat people.
Similar to the race of men, save for their short, light-colored fur, the Ohmes-raht may easily be mistaken as men at a distance. Unlike the many other species of Khajiit, who walk, like cats, upon the balls of their feet, the Ohmes-raht walk upon their heels. The Ohmes-raht are most likely the type of Khajiit usually encountered in Cyrodiil.
I've never mistaken Oblivion's Khajiit for anything except Khajiit. And the Khajiit we see in Daggerfall appear to be Ohmes-raht, they looked very different from Oblivion's Khajiit.
Morrowind's and Oblivion's Khajiit cannot be the same breed. The head shapes and fur patterns greatly differ.
Every race in Oblivion have gone through changes between Morrowind and Oblivion, it doesn't mean anything, and not all cats of the same breed look the same, this can be true for Khajiit too. I'm sure not every Khajiit of the same type has an identical pattern, but due to limitations of game mechanics, Bethesda couldn't represent this in Morrowind.
They have horns, the armorer in Balmora has a face with horns. If you don't want to call them horns we can call them blunted feelers.
I wouldn't quite call them horns, more like horrible growths that are hopefully lethal. Unfortunately, I think they're natural.
Either way, I'm thankful that Bethesda changed
that about them.