What a ridiculous statement. Cech has who in front of him? Terry, Carvalho, Alex, A.Cole etc. Also to dispell an misconception Buffon is twenty-nine, Casillas is twenty-six and Cech is twenty-five. It's hardly a 'huge' difference, the difference comes from the fact Buffon has been playing top flight football since he was seventeen, as has Casillas. Cech didn't get to one of the big leagues until he was twenty-two.
Cech makes a number of saves a lot harder than they should be, he relies on his reflexes and height to make a lot of saves. If he improved his positioning he's save even more shots, often his positioning is slightly amiss. Currently that's ok as his reflexes and reach can compensate, when he's older and his reflexes begin to fade he'll struggle more.
When all is said and done all three are fantastic goalkeepers, but if I went for one it would certainly be Buffon.