The rest of the family catches up on birthdays at major family gatherings. For example, at Thanksgiving or Christmas, all the kids with birthdays from about mid-summer through the end of the year will get birthday gifts from those who forgot; at a summer BBQ, the early part of the year is covered.
My family does that too. We have 9 kids in the youngest generation now. The 1st birthday thing has been done to death. Now we're rounding out the First Communions. Next big milestone will be graduations, I guess.
I tried for years to foster family togetherness after my mom passed away. I'm the youngest of the family and without kids, but for some reason I thought it was my job. I guess my mom trained me too well (or my dad just sucks at it too much).
Sometimes it works and sometimes it doesn't. The problem is, unless you are directly involved in each other's daily lives (like live next to each other, go to the same school or work) it can be near impossible to schedule each other in.
Personally, I have gotten peeved going to the effort of remembering the family's occasions because I knew they never acknowledged mine. (Only my sis makes an effort to remember my birthday every year. And her boys pick that up from her.) But then I started going to Disney for my birthday. Now Mickey can remember and I get to celebrate for a week.
Another thing I do to help foster that togetherness is setup every family with a webcam and Skype account. My nieces and nephews love being able to virtually visit with each other. My dad's Skyped them to share a bedtime story. I've had early morning pre-school conversations with the kids. And we even organized a story round robin for Thanksgiving, which the kids read aloud at the family gathering that weekend.
But try to arrange a sleepover for the cousins or gathering to celebrate my dad's and brother's birthday (they were born on the same day of the month) and you run right smack dab into the Conflicting Family Schedules wall. That's why I say families do their best but can fall short. Maybe the one good thing you can say about a family is that the door is always open. Extend an open invitation and there's always hope.