Now THAT'S sensible. It also virtually encourages piracy (how else is one likely to get in depth comparisons of voicework) - I despise piracy and that's why I preferred to simply ask the developers whether the voice acting released was indicative of the final product. It also means pre-ordering is out (which is a pity, because I usually try to support Obsidian games as much as possible).
It only encourages piracy if that's where your mind goes. I don't pirate either, but there will be no shortage of increased samples and opinions of the game once it gets released. I don't see how it encourages piracy at all. Unless you feel you must have the game at release. At which point, I must contend that the current sampling of dialogue really isn't that big of a deal for you.
Buy the game when it comes down in price. Which is also one thing I was hinting at. You're not a slave that has to buy a game you have reservations about at release.