Though it may seem ridiculous that Microsoft would name its new console without already owning the domain name for it, there are a couple of mitigating factors here. One is that the guy who owns XboxOne.com registered the name almost two years ago. That's some good guessing!
Fusible reports that Microsoft has filed a complaint with the National Arbitration Forum over the domain name to thwart the lucky cybersquatter, whom records say is a resident of the U.K. and registered the name in December 2011. XboxOne.net also is covered in the same complaint, indicating it is owned by the same person, Fusible notes.
Domain registrations are public (indeed, Fusible sniffs out all of them for clues on upcoming games, movies and whatnot). Worse, to have entered into a legal dispute over ownership of a domain name for which no product or service currently existed, would have tipped off everyone what Microsoft was going to call its next console. So the company probably figured it just had to suck it up and battle this thing out after they announced the device. Microsoft seems to have done well in these disputes anyway.