The cloud is not a central location, it is distributed.
Service Oriented Architectures allow an application developer to cherry pick services available from disparate distributed locations knowing that the interfaces for each will be well defined (using WSDL or the like) and the transport mechanism ( e.g. SOAP over HTTP) will play nicely and not require custom translation of inputs and outputs.
There are plenty of good examples of SOA or "the cloud" other than some naff web site which badly replicates something I can do locally. An example I recently coded is an enterprise wide token based authentication which allows field engineers access to our remote equipment via a web service. So
- engineer - contacts "cloud" (i.e an RBAC webserver), gets token, attempts handshake
- kiosk - sends token to cloud gets credentials, allows access.
"Mainframe" not necessary.