My first question is, what actually looks unpolished that's been released so far? It's an Elder Scrolls game, it's not about handling every detail that can arise out of the tens of millions of variable configurations, it's about those tens of millions of variables. I take all the screenshots and video released at "Release Level" quality, and sure, it's not perfect, and might be fixed, but if it's not, it's still better than 99.82% of the games out.
Anyway; Pre-Alpha, to my understanding, means a build of the game where features are still being introduced or cut.
Alpha; the features of the game, baring some catastrophic conflict, are locked in and the Technical Polish-Optimization, and ongoing bug fixing issues go full tilt when the whole team finally have an idea of exactly what they have to work on in detail.
Beta; Most of the really bad, game breaking bugs are squashed. The game is, theoretically, a market viability. And an alarming number of developers are releasing "Beta" versions and patching fixes in*cough*ObsidianEntertainment*cough*. Balance issues, difficulty curve, and advancement pacing are usually dealt with here. Some ongoing bug and optimization too
Commercial Build; Whatever makes it to the production line is the Gold version, but a commercial build is the one that's actually ready for commercial release. IE, not New Vegas.
All in all,Skyrim is looking out to be a solid game.
Sorry, but Crash Bandicoot is a Solid game. If Skyrim is a just a "Solid" game, it'll completely destroy the company. So for everyone's sake, you'd best be wrong.