Why would you want a hard drive that big? Unless you have a second one and are running RAID then I don't understand it.
Think about it, if you have that big of a hard drive then you will probably put all of your files on there. Then BAM if/when your hard drive fails you just lost a massive amount of stuff. That is a huge risk. I don't think they should sell those things by themselves, they should sell them in packages of two so you can have one as a backup.