I don't think it is quite as simple as an excuse for a party. Although I am an atheist, I think that secular society benefits from having a few 'rituals' such as naming ceremonies, to acknowledge important events.
A 'naming ceremony' is probably less about giving the name, but more about the opportunity for the important people in the baby's life to come together to acknowledge the baby's life, congratulate the parents and stop for a moment to reflect together on the parents' hopes and dreams for the child. This probably goes even for those who say they just like an excuse for a party!
Having said that, I haven't arranged one for our ten week old baby, but wonder if I am doing her a disservice, as she won't have anything such as photos, cards etc to look back on. However, I am thinking of keeping a little notebook to add my thoughts to ever year on her birthday, and maybe ask others to contribute to, then she can have it when she's 30 or when I die or something!