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.
![Very Happy :D](http://gamesas.com/images/smilies/icon_e_biggrin.gif)
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.
![Razz :P](http://gamesas.com/images/smilies/icon_razz.gif)
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.