What if you are a Fortune 500 company, or a part of the government? A defense contractor? Heath insurance provider? I work for a company that does "private cloud", mostly large enterprise/government places that want the flexibility of having their data accessible anywhere, but are not willing or able (for security reasons) to have Amazon or some other provider host their data. If you already have data center infrastructure and expertise in-house, the long-run cost and benefits of buying your own hardware for high-traffic applications can often outweigh renting space and/or paying on a per-transaction basis from AWS. Public cloud is great, but it's not the right solution for everyone.