Wow. This is a really rough subject. I do understand the differences in cultural customs, but when your family came to America did your dad think that his children would not eventually be affected by Western influences and traditions?
Even if cultural differences weren't part of the issue, this seems like such a weak subject for him to take such a strong stance on. I'm really having a hard time wrapping my head around his ultimatum. He may be disappointed, hurt, angered, etc because he doesn't understand, but I would never think this would something that would cause a parent to separate themselves from a very important day in the life of their child. Honestly- there are worse things.
Just out of curiosity, does your mom have his last name?
Hang in there. I bet he will eventually come around. I hope your family points out how petty and foolish he is being. Get with the times, pops.