I had the same question. Why aren't the birthdays being celebrated with the same potlucks that your "regular" grad-student parties are? Or are these faculty/staff birthdays, to which the grad students have been invited? And yes, as grassy asked, how many people are we talking about, that there have been so many big "life events"?
No, just grad students. For the life events, there are first events just for grad students and/or entire department, but there are other events in addition that include both grad students and non-grad folks.
One additional question: Leaving aside the money, where do you all get the time for all this celebrating?? My doctoral community (both students and faculty) was very closeknit and liked socializing together, yet we rarely found the time to have more than one or two parties (for whatever reason) a semester. Any other socializing (lunch, the rare dinner-and-a-movie, etc.) was generally squeezed in one-on-one or in very small groups (three or four people, plus, for some things, any SOs), so that there'd be fewer schedules to coordinate. "Life events" (the occasional wedding, babies, etc.) usually involved individual gestures, such as an emailed congratulations and, among the closest of friends, perhaps a small gift.
With respect to time, I don't know. You'd have to ask the hosts/hostesses. I often wondered about the time thing myself.
Because of the time constraints, when we did celebrate things, we often combined events, except for proposal and diss defense celebrations, which always occurred within hours of the defense. (For these, the candidate's advisor usually paid the candidate's way and often partially or fully subsidized the drinks and/or food for everyone else.) My birthday, for example, fell within two weeks of two other student birthdays, so one year a fourth student hosted a merged celebration (potluck at her apartment) for us. The only "gifts" were the food and drink and good company--and multiple birthday cakes, an extravagance for us. Most years, my birthday (and most others) passed with no formal celebration, because no one had the time for a party.
It sounds like you have a really integrated department culture. It almost sounds like a family. That's great. We have a few graduate students in my department who transferred from other institutions, and they note that our department culture is quite different from their former institutions. One student described a culture quite like yours.
