Here's a strange thing. The domain ModernWarfare3.com links to a Battlefield 3 website. A WHOIS lookup for the MW3 domain reveals the registrant as Domains By Proxy, Inc., a GoDaddy-owned company that offers domain privacy services. Interestingly, this particular domain was registered all the way back in March 2009.
I'm no expert on domain registration, so I'm not even sure if it's possible to buy a domain and redirect it to someone else's website. Given how far back the domain registration goes though, long before either Call of Duty: Modern Warfare 3 or Battlefield 3 were announced, it seems that this has been planned for awhile. Or maybe not.
Interestingly, if you search "modernwarfare3.com" on Google, the first search result -- www.modernwarfare3.com -- is clearly describing a Call of Duty website. Click it though, and you're whisked off to a Battlefield page. Given that, I would say it's a safe bet that outside parties, probably one or more hackers, are behind this redirect.