The hosts always have an idea of about how much bandwidth you'll use, even if its unmetered or unlimited. They calculate it by your max speed by the duration of a month. So if your server allows maximum speed of 100kb/s with 'unlimited' bandwidth for a month, it just means you're getting around 259.2gb bandwidth per month.
Its only a matter of wording to make the deals sound better than they are.
And contrary to what everyone said previously, Dreamhost is a TERRIBLE host that, while has good HDD and bandwidth, has terrible customer support. And a lot of people break the rule of too many CPU minutes, and Dreamhost never proves it, but after the 97 day money back guarentee they notify you of the situation, suspend your account indefinitely and take your money.