1. You need strengthened and widened runways and taxiways to handle a plane far wider than the 747 and also weighing around 1 million pounds!
2. You need a terminal gate with increased handling capacity for the plane.
3. You might even need to increase wake turbulence separation for the the A380.
Small wonder why airlines are finding the 777-200LR, 777-300LR, 787-8 and 787-9 vastly more attractive, since they don't need expensive revamping of most current international airports.
As designed and flown it doesn't have the structural strength or power to deliver as promised; once they factored in the extras (showers, clubs, stores, etc) it would be overweight, underpowered and structurally weak. That is why they immediately had to delay the intended rollout date...and the modifications are going to cut into cost/performance estimates.
It's a design dinosaur, taking 40 year old design and construction to an extreme.
It's inflexible for changing routes. Yes, an airline could condense two-three flights into one, however, it can't work backwards. If that route is suddenly less productive you can't leave one third of the plane at home. Also consider the fact that you now offer one flight time a day, not two or three like your competitors.
Lastly, look at the L1011. It was one of the best airliners ever built. Soon after it started operating one went down in the Florida everglades when a 5 cent light bulb burned out...and pilot error. Because of the high loss of life and media coverage orders for this new plane dried up over night, airlines already flying them sold them off and the company building them eventually went under. WHEN a 380 goes in it's going to be horrible.