Its necessary to have automation at 30,000ft because RVSM airspace starts at FL290 and goes up to FL410, and the FARs require use of an autopilot for cruise in RVSM airspace.
Most airliners fly at or between these altitudes which requires use of an AP, and many airline FOM/GOMs require or "strongly suggest" use of autoflight systems during most phases of flight.
I hand flew at FL450 while part 91 once; of course that was a bizjet and not an airliner but somehow I'm still here to talk about it on the internet.