startx is a shell script. The vast majority of distributions don't use it at all - they use a display manager that then does most, but not necessarily all, of what the xinit system does (plus some extras, depending on the DM).
startx from a VT should give you an X server. You can get from there to a standard session (minus the DM) by setting the appropriate environment variables and making sure the right session manager is executed.
I don't call that 'no configuration' though. And if you want to startx into Fluxbox you also have to make sure that all of the aforementioned services are run (unless you're totally abandoning your Desktop environment, in which case this whole conversation is pointless).