Not an answer, but a workaround:
For what it's worth, I've wired up CTRL+SHIFT+P as a shortcut key against the Publish menu item, so while I am not "Publish automatically upon build", at least it isn't too much effort. Note that publish performs a build as its first step, so for me now CTRL+SHIFT+P replaces CTRL+SHIFT+B for this particular project.
I wonder if, given that Publish includes Build as its first step, that it is not possible to publish as an MSBuild task because it would result in a "circular reference" of sorts, building forever. Just a thought.