If their description is correct and Argonians are in fact reptilian, they are cold-blooded. Highly evolved or not, reptiles rely on exothermic methods to produce heat. Now that's not to say they can't alter the viscosity of their blood to survive in extreme cold, but it would also place an enormous amount of strain on their cardiovascular system, unless of course it is also adaptive.
For the last time, they're beings created by freaking sentient trees that have lived on Mundus when men and mer were the same. They're controlled practically by hive mind by these trees when they choose to do so, and act as a way for these trees to interact with the outside world. Being reptile is superficial at best right now, because the argonians are just extremely alien to all other beings in this universe so far, let alone Tamriel. Hell, they're not even related to men and mer at all, only these sentient trees.
In short, argonians are too weird, behaviorally, psychologically, and physically to assume anything other than what has been stated through books, lines of dialog (not greetings), and dev posts.
Again, he's a dev post (Mark Nelson) that sums up the "never assume" thing with argonians
Never underestimate the adaptability of Argonians, or, more specifically, the power of the Hist to allow Argonians to adapt.
I wouldn't expect to hear an Argonian born in Skyrim (or on Solstheim, for that matter) mention being hatched. Nor would I expect to hear more transient Argonians (say, members of a small, nomadic tribe) speak about laying eggs. However, in warmer climates, in places with established, stable, and permanent communities, you would likely see a great number of eggs.