Emre,The ES is often used in extremely large environments and was written from the beginning to allow a SaaS model, fortune 500 companies, or government agenies to have centrally stored database environment without the limitation of growth or size. We had this need in our medical software as well and we use it every day in large environments....and it is solid! The ES fully supports OLTP and even works when running in a server farm when load balancing is implemented.
The ES obviously works for smaller environments as well, but it was designed to be scalable by hardware and run in a server farm environment preventing a cap from being hit and providing the most scalable environment.