OpenStack has been gaining a lot of momentum. There is little to dispute this. When you install OpenStack, you get a private cloud solution that builds on top of libvirt to support Xen Server, KVM, VMWare, HyperV, and many more hypervisors. What a lot of people do not realize is that OpenStack speaks Amazon WS REST APIs. OpenStack supports EC2, and S3 and a lot more as well as its own OpenStack REST APIs. In fact the install guide for OpenStack even has you download euca2ools (from the Eucalyptus) and this is what you use to spin up instances and manage EC2, S3, EBS, virtual networking and more.

OpenStack does not fight with the 800 lbs Gorilla. It adopts it, and adapts it. It re-purposes it.