I think, as a term passed to non technical or lightly technical end-users, "the cloud" is largely useless. The cloud is not an "end user" feature except in the features that a cloud-based architecture might bring.
Taking your example - end users should never hear about "the cloud" when discussing email. All they care about is a hosted application that "just works" - having it based "on the cloud" is uninteresting, except by the features it brings with it, which they reap the benefits of.
So, maybe trying to use it when discussing things outside of mostly technical (IT personell, Devops folks, developers) is mostly useless except to denote a very specific (scalability, uptime) set of features and even then you're better off not talking about "the cloud" but the specific features, which are tangible to them.
They are CIO's and managers in charge of purchasing an email solution. They know they need a "cloud strategy", and vendors are quite happy to tell them their solution is "cloud based" if it make them happy.
So yes - it's mostly useless as a technical term.
Take for example, cloud storage. I would not sell "the cloud" part to a person, rather, I would sell them the fact that it's hosted and highly reliable, infinitely scalable, pay as you go and cheap compared to a local storage cluster buildout.
I wouldn't sell them the cloud part, as not all things in, on and around the cloud inherit all the features the cloud might bring (meaning, you can screw up an architecture no matter where it's implemented).
But unfortunately many times the people with the budget don't actually care about the features. The word "cloud" is important to them because their CEO read about it in a glossy magazine, so they need to be "cloud enabled"
You need to be careful, though because sometimes "cloud" is seen as a negative. I've seen companies that state "We don't believe in the cloud and we have a purchasing policy that excludes any cloud based solutions" - but then you dig deeper and find how proud they are of the "hosted solution" they bought from a vendor because of the way they don't have to pay for capacity until they use it.
Sigh..
(Advice for young players: Enterprise sales will kill your soul)
Yes.
We have a word for that - Internet.
You noticed that? :)
I think a much more apt - and something more applicable to SFDC, is anything which exposes "architectural resources" - such as Platform, Storage, or Compute as a service/hosted system is a much better, and cleaner a term then throwing applications built on cloud technology into the mix. The cloud is the dynamic, elastic, "on demand" of resources, not the utilization of those resources.
I think you are right, kind of. Developers talk about cloud computing, cloud storage etc to distinguish it from their traditional services.
However, non-developers don't see it like that. They see "email" as a resource, and the ability to elastically grow their email service as making it "in the cloud".