Do modern aircraft automatically manage the deceleration to Vref?
This depends on the aircraft.

Airbus aircraft have a managed speed mode in the FCU (flight control unit), where the speed is completely controlled by the FMGS (flight management and guidance system). This includes slowing the aircraft down when the appropriate flaps are selected by the crew. No manual action is necessary to reduce airspeed for landing until you hear "RETARD, RETARD" during the flare and pull the thrust levers to idle. See here for some details.

Boeing aircraft can also manage speed automatically in VNAV mode, but not all of them slow to reference speed automatically, only to the flap maneuvering speeds when flaps are selected by the crew. When using other modes than VNAV for the approach (like APPR for an ILS approach), speed must always be set manually in the MCP (mode control panel). For an RNAV approach, this may be possible, see e.g. from the 737 NG FCTM (5.46 Approach and Missed Approach):


  When on final approach, VNAV may be used with speed intervention active (as
  installed) to reduce workload. Adding speed constraints to the final approach
  waypoints is normally not needed and causes extra workload without providing
  any safety benefit. This also reduces the ability to make last minute approach
  changes. However, if needed speed constraints may be changed if the default
  value is not suitable.