It looks like some people are taking the word "unlimited" too literally. Of course disk space or bandwidth can never be unlimited and same goes with domains, databases etc. Marketers and companies often use unlimited when they want to tell the customers they don't have to worry about their disk space or bandwidth usage.
Unlimited resources often come with certain limitations and fair usage policies to ensure no one is using too much server capacity and to keep it "unlimited" for everyone else on the same server.
Yep. What many don't realize, and some web hosts (sadly) are unable to grasp, is that "unlimited" refers to the "hosting resources" that are found in the "hosting plan," which are traditionally limited by QUOTAs. The hosting resource becomes unlimited when that traditional quota is removed.
And it cannot be over-stressed that those fair usage policies are the same ones limited hosts use.