Google-calendar – Why do birthdays show up in the calendar

It is unclear what special feature you want a yearly event does not provide. My suggestion is to create a new calendar, label it something like "Anniversaries", then start recording yearly events.

On the other hand, birthdays are supposed to be recorded to Google Contacts. However, all birthdays show up in Birthdays Calendar and I'm not aware of an easy way to hide certain people or circles from the list.

As of now, Facebook does not provides any such option, so it is not possible.

At the maximum, Facebook does has an API, so it must be possible through the API, but then, you have already gone through the apps and they are providing only dynamic links and not actually copying the data.

So, what you are left with is - make your own app to copy birthdays using the Faceboom API or else, you can always manually copy and paste the data from Facebook to Google Calender or may be iCal or any other software system of your choice.