I would dispute that Americans alone adore celebrities, it is a phenomena which affects most humans to some extent.
I would guess that it is in part we see celebrity as a measure of success. By becoming a celebrity they have found a key to success and so if we listen to them then maybe we too will have that key to make ourselves successful.
Of course the idea of success being something we can all achieve is a fallacy. Some people who become celebrities have natural ability, some work very hard for many years to achieve a goal, not neccessarily celebrity status maybe a top sportsperson or actor. Others merely latch on to others celebrity status in order to gain celebrity status or notoriety themselves.
Even in ancient cultures people adored people whom they saw as fulfilling ideals of success. In Ancient Rome a gladiator might achieve celebrity status by bravery and victories in the games. Warriors became heroes another variation of celebrity all we need to do is read ancient texts and compare how heroes had all the answers much as celebrities do today, according to the tabloid press and fan blogs.