provided vs exposed
If you're offering infrastructure as a service, you have to have infrastructure to offer and it has to be exposed.
But if you're offering something else, then:
The infrastructure doesn't need to be exposed, THUS you don't need to have it.
- You offer VMs, so you need to expose VMs, a management console for VMs, and (hopefully) APIs to connect to and operate them
- You offer a runtime, so you may or may not have VMs--but who cares since what you need to expose is the runtime, a management console for that runtime, and (hopefully) APIs to connect to and operate it
- You offer an application, so you may or may not have VMs or a particular runtime--but who cares since what you need to expose is the application, a management console for that application, and (hopefully) APIs to connect to and operate it
It gets a little more complicated when someone wants to build something else on top of what you offer. Then they probably want and/or need more exposure to, and more control knobs for, the underlying stuff.
Basically, this is what makes IaaS (specifically VMaaS) different in kind from anything else.
What you provide guides what you expose dictates how you can build.
What you've built limits what you can expose dictates what you can provide.