Inlaws and the rest of us

I've been contemplating the delicate situation that is inlaws since I read Tracy's post this morning. Supposedly some people manage to marry into a family that is virtually the same as theirs and the transition into their new family is smooth as can be. I just don't know anyone like that myself. It seems like most of the time, becoming a member of a family you did not grow up in is a shock to the system that just keeps on shocking.
For starters, I am perfectly grateful that I'm not having the same inlaw problems that Tracy is. That on top of all her other troubles is just too extreme. I'd have cracked long ago if I were in her place.
That said.... I've still got a handful of issues. Things I just don't understand. (Disclaimer: I love my inlaws very much, even if I don't understand them)
My family likes making a big deal out of things. We celebrate birthdays, we get excited when someone accomplishes something, we show up when invited to special occasions like baptisms, weddings, and baby blessings. Renn's family - they just don't care. His grandpa is turning 80 next week. If I live to be 80, I expect to have a huge celebratory shin-dig. But for whatever reason, nobody else thinks it's a big deal that Grandpa is having a birthday, let alone that it's a milestone number, let alone that his health is not-so-hot and it very well may be his last birthday. Nope, no parties being held here. Renn and his dad and I will drive up there all by our lonesomes and have a very small celebratory dinner and then drive back. The whole thing makes me sad and a little sick. ( Oh wait, I was already sick... never mind.)
So somehow I married into a family that doesn't celebrate birthdays, doesn't exchange gifts on Christmas (they do give some gifts... But they don't really wait until Christmas to open any of them), doesn't get excited to see each other, and are generally disinterested in all things I associate with family bonding.
Lest I lead you astray into thinking that they are horrid, let me clarify. One SIL spent Thanksgiving day on the phone with a friend in her bedroom talking about how "if she'd been thinking at all she would have volunteered at a soup kitchen or something instead of staying home." This was on one of the rare occasions when we had actually managed to get more than half of Renn's siblings together with his parents to celebrate. Nobody (except me I guess) really cared to be there. Even when they are all there, it's like they're not giving 100% - they are somehow distracted (by what, I do not have a clue.) They are good people and they do good things, it just seems to me (an outsider) like something is missing.
But does everybody feel that way about their inlaws? They are not like our family of origin so something seems to be missing? I feel guilty that I feel this way about my new family. I feel sometimes like they are silly or shallow because it feels like they are missing out on so much that matters so much. Is it all in my head?