Penelope Trunk says:
Diversity in the workplace is not “diverse religious expression.” Diversity should express itself in how people approach business problems. Religion is not appropriate at work in the same way that politics is not appropriate; both are divisive.
Corporate events that are tied to religion make people who don’t practice that religion feel like outsiders and therefore inhibit diversity. (And those of you who think Happy Holidays is non-sectarian, please realize that almost all non-Christians I know hear “Happy Holidays” as “Merry Christmas to those of you who do not celebrate it.”)
Heh. I guess it's not such an issue for us in India. We happily get holidays for all religious occasions (Hindu, Islamic, Sikh, Buddhist and Christian) and are quite enthusiastic about celebrating them in office.