You should also be able to pull 'latest' as well, correct?

I think the problem with specifying just 'apline:3' is that it is an ambiguous statement. Do you want alpine:3.0? Or do you want the latest in the alpine:3.x line?

I think either using 'latest' or specifying a particular point release is what you'd expect.

Edit:

> [... ]people do alpine:latest in their Dockerfiles, cross their fingers, and hope for the best.

What are you crossing your fingers for? alpine:latest should be the latest stable, and should work as intended.