If they are fully lizards with cold blood, and they come from a warm marsh like home land, wouldn't they drop dead from the constant freezing cold?
I mean yes the sun shines in Skyrim, but it can't be enough to heat up a huge lizard body every day.
I like to think they are warm blooded.
Think of it this way, they aren't humanoid lizards, they are lizardoid humans? lol
*edit* Plus the hist grants them adaptative abilities. Which is why you see Argonians with feathers in skyrim to help keep the heat in.