Cold blooded / warm blooded is really just a false dichotomy, which no modern biologist would be caught dead using. The amount of heat produced by an animal's metabolism, and that animal's temperature stress tolerance, is very fine-tuned and varies from individual to individual.
More relevantly, humans cannot survive unaided in the sort of extreme colds Skyrim is supposed to have. They get by with external devices such as fire, thick clothing, and shelter. I imagine Argonians do the same.
What you said is dead on, but even MORE relevantly, Argonians are NOT precise anologues to real-life lizards. They're bipedal, sentient, capable of vocalization, and can cast fireballs from their fingertips.
It continually astounds me that this one minor detail of "cold-blooded/warm-blooded" is what so persistently trips people up, in light of those facts.