They're not huge like the dragons of many other games. They're more like wild animals than a dude in a winged lizard suit, too (they've been animated to appear driven by their instincts rather than intellect, although I do realize Skyrim's dragons have been stated to be intellectual creatures.) I personally like the Skyrim dragons more than most others for precisely these reasons. I have no notion of these dragons being 'realistic' however, as a long tail is suggested by Earth's fossil record to be a major size penalty in flying vertebrates (Birds, bats, pterosaurs.) Then there's also the fact that they breathe fire, ice, and possibly other elements.

Even if these dragons appear to follow their instincts and aren't ginormous or six limbed, I wouldn't call them wyverns. Bethesda calls em' dragons, and fiction-makers can call their critters whatever they want.

If a developer/authour has not named their creature, I will call it a wyvern if it possesses venomous barbs, has only four limbs, no breath weapon and/or is not intellectual. I call it a dragon if it has six limbs, no venomous barbs, breath weapons, and/or strong intellect. If these traits are mixed together, I tend towards calling it a dragon.