You're probably right. The server IP gives it away as well. However, that's not part of the domain registration information. Many people here look at it and just see "oh GoDaddy and DomainsByProxy so it can't be Blizzard" and that's just wrong. Blizzard uses both those services as well. The server IP is not really part of the domain whois though but "additional information". And yes, that gives it away. But again, the pure domain registrar info does not tell us anything about whether it's Blizzard or not.
(Caveat: Blizzard could be using something like cloudflare.com which hides the original server IP. I'm doing this as well for some of my websites, so some of my websites state in the whois that "100+ other sites are hosted on this server" when in reality it's a dedicated server as well. I do not know, however, if Blizzard uses such a service; to my knowledge they don't.)
But this entire discussion is getting quite ridiculous and reminds me of stupid Stackoverflow discussions (granted, on there it would've been closed many days ago). I'll keep this thread open though because the URL was just recently posted on Reddit in other subs by people who still believe this is real.
It's fake. Because of the pure website's coding. Because you wouldn't hide the message when the URL already tells you everything. Because of the server IP. (But the domain registrar doesn't tell us anything at all, so stop posting whois records.)
Yes, this is probably fake. But I'm not sure what everyone is trying to show with the domain whois? GoDaddy is a popular registrar in the US, and DomainsByProxy is a service provided by GoDaddy to "hide" your registrar information. It's simply a placeholder for privacy reasons that anyone can order. If Blizzard were to buy a domain and they don't want to disclose it yet, they might use this service. And once the game is officially confirmed they could update the registrar data (or simply cancel the proxy contract which has to be renewed every year anyways). But citing the GoDaddy entry 3 times doesn't prove anything, just look at the official Diablo3.com entry which looks the same (except for no proxy data as there's no reason to hide anything).
A giveaway for fake though is the source code of the website. Super minimal HTML code, inline CSS, and doesn't look like any HTML code I've ever seen on a Blizzard website. The only instance I can remember seeing such sloppy/minimal website source code from Blizzard is when they hid hints to future release in the source code (as they did for the hidden lost numbers in the splash screen code that led to a hint at the D3 announcement). It also doesn't make sense to hide anything (domain owner, image, or some HTML code puzzle) if the very domain name already reveals everything...
So yeah, probably fake, but not because of the whois, but rather because of the website and its code.