As we all know, the beast races have gone through major changes from game to game. Strangely enough, these are not retcons, but different subspecies.

A khajiit's breed is determined by the lunar phases during their birth. Argonian breed is determined by how many times they lick the Hist tree.

Game - Khajiit breed
Arena - Ohmes (identical to Bosmer)
Daggerfall - Ohmes-raht (similar to Bosmer, except with body fur, cat ears, and tails)
Morrowind - Suthay-raht (bipedal cats with claws, digitigrade feet)
Oblivion - Suthay (identical to humans, except with fur, animal heads, and tails, no claws, plantigrade feet)

The Argonians in Arena may not be Argonians at all, but Kothringi tribesmen; it is widely rumored the Kothringi were hybrids of Argonians and Nords. Daggerfall and Oblivion, interestingly enough, used the same kind of Argonian: anthropoid lizards with plantigrade feet, and females with boobs. Morrowind-type represents the farthest difference from human anatomy.

There is no explanation for why all beast race members in a particular game are of the same breed.

If possible, it would be great in Skyrim if there would be several breeds for Khajiit and Argonians, giving more variety, i.e.: Ohmes-raht and Suthay-raht.

I've got to say that I didn't like how the Argonians looked in Arena, they looked like zombies to me.

In terms of how the beast races were presented, Morrowind is my favourite, as they were more beast like what with their legs, etc. I really love how the Argonians look in Morrowind.

I don't know the lore all that well and I haven't read Infernal City, but I don't think there should be a lot of Khajiiti on Skyrim...

Oh, that one's easy: technical and time constraints.

The only game where the breed of Khajiit is explicitly stated, to my knowledge, is Morrowind.

And as far as I can glean from lore, the difference between a breed (such as the Suthay) and it's like-named breed (such as the Suthay-raht) is size. There is NOTHING stating they differ in appearance in anything other than height.

http://uesp.net/wiki/Lore:Khajiit#Morphology

Except,

"Ohmes

Similar in many ways to the Bosmer, although generally of lesser stature. In order to avoid being mistaken as one of the Bosmer many Ohmes tattoo their faces to resemble a feline-aspect. The Ohmes is the most common form seen outside of the province of Elsweyr, taking advantage of other races' preference to their appearance to serve in positions of ambassadorship and trade. It is possible that the Ohmes are the type of Khajiit in Arena.

Ohmes-raht

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 in the game Daggerfall."

...and,

"Senche

The Senche is commonly employed by the other Khajiit breeds as a steed, assumedly by will. Roughly the same height as the average Altmer, with an average weight comparable to that of twenty Altmer.

Senche-raht

Larger and slower than the Senche, the Senche-raht are also possessed of a shorter body-span and straighter legs. The average Senche-raht stands as tall as two Altmer and can weigh more than fifty. Like the Senche, Senche-raht are also employed as steeds, notably in battle, whence they earned the title "battlecats" from Imperial troopers."

Plus, little has really been seen of most breeds of Khajiit.

There isn't really much of an actual explanation for it, other than the fact that putting them all in would require so much extra time and work on their part, plus it would then seem like they're showing some favoritism toward the Khajiit, and people would [censored] and moan about it.

Now, if they ever get around to setting one in Elsweyr and we don't get every breed in the game, I'll be rather disappointed. :/

I actually liked the Argonians in Daggerfall best. They looked quite formidable, lithe, and almost dragon-like. But the Oblivion ones looked a little too human in their bodies. I think it would be GREAT to have subspecies, maybe with certain pros and cons for each. That would give great reasons to play beast races, which seem to not get much love from a majority of players.