async/await are just sugar over the much older asynchronous delegate pattern that has been in the language since day one. So yes, they were.

are they widely used in APIs to e.g. send a query to the sql database or open a file?

Yes.

In .Net 4.5 there are Async versions of the web, file, stream, image and SQL category of functions.

It's also making its way into ASP.Net layer.