Well, also Buffon on his own right is unique.
Del Piero for us is a legend, but looking it at the big spectrum, he is just one of a bunch of superb forwards and is not even among the top ones, like Messi and Cristiano, just talking about numbers because in talent IMO prime del piero had nothing to envy to those 2, in fact i just have seen one player who was more inventive and intelligent than him and that was Zidane. Thats how high i rate Del Piero. He was unique in some sense.
But Buffon is at the indisputed top of his discipline. Also, like Baggio said, he has been around FOR SOOO LOONG, that people that do not follow serie A or Italy, reacdt like "Damnn!!! Buffon still plays? i remember him when i was a kid" and comments like those.
He is 38 and still is rocking it. Its unreal to be honest.