In diesel engine fuel supply systems, unit pump & unit injector are operated by camshaft & hence pressure of injected fuel depends on engine speed. Whereas, in common rail systems its independent of engine speed. Still, are unit pump & unit injector used in modern automobiles?

Yes. But the pump doesn't always run from the cam itself but from a gear. That is how you can adjust timing the injector pump to a rich or lean condition. By advancing or retarding timing of the pump.