Why is it more difficult for ATC to manage a larger airliner?
They must leave a greater amount of time in between landings/take-offs as the size of the aircraft increases due to wake turbulance

There were historically 3 classes of aircraft for the purpose of wake turbulance classification


H (Heavy) aircraft types of 136 000 kg (300 000 lb) or more;
M (Medium) aircraft types less than 136 000 kg (300 000 lb) and more than 7 000 kg (15 500 lb); and
L (Light) aircraft types of 7 000 kg (15 500 lb) or less.


With the introduction of the A380-800, where it is near MTOW, a fourth category has been added


Super Heavy for Airbus A380-800 with a maximum take-off mass in the order of 560 000 kg


How much time must be left? Well that depends, for an A380:

Arriving Aircraft


  
  MEDIUM aircraft behind an A380-800 aircraft — 3 minutes;
  LIGHT aircraft behind an A380-800 aircraft — 4 minutes.
  


Departing Aircraft


  3 minutes should be applied for a LIGHT or MEDIUM aircraft and 2 minutes for a non-A380-800 HEAVY aircraft taking off behind an A380-800 aircraft when the aircraft are using:
  
  
  the same runway;
  parallel runways separated by less than 760 m (2 500 ft);
  crossing runways if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 300 m (1000 ft) below;
  parallel runways separated by 760 m (2 500 ft) or more, if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 300 m (1 000 ft) below.
  


Source for timings: http://www.skybrary.aero/index.php/Airbus_A380_Wake_Vortex_Guidance