You are correct, if you have no need to add additional servers or scale the platform, have predictable bandwidth and storage requirements, and your sysadmins don't mind patching all the base OS instead of just rolling new VMs.
However AWS allows you to accomodate uneven growth and load. You can create new machines in minutes (or half an hour for Windows). The virtual nature allows you to quickly ditch a broken host for a good one. You can also save money on development infrastructure by switching it off, or run background jobs on spot machines. Then there's the other services available such as S3 and Lambda.
Of course there are other clouds worth considering, but the advantage of cloud infrastructure is the ability to call it up without months of lead time.
However AWS allows you to accomodate uneven growth and load. You can create new machines in minutes (or half an hour for Windows). The virtual nature allows you to quickly ditch a broken host for a good one. You can also save money on development infrastructure by switching it off, or run background jobs on spot machines. Then there's the other services available such as S3 and Lambda.
Of course there are other clouds worth considering, but the advantage of cloud infrastructure is the ability to call it up without months of lead time.