I feel this is part of the FB generation. Somehow it's become for them that something is not "real" unless it's been lauded on FB. I see this all the time: birthday wishes and pics of presents, thanking people on FB (wtf happened to a phone call or a thank you card?), posting anniversary things publicly on FB for everyone to see (like wtf you didn't marry everyone you married your SO) etc... It's just part of the "attention whore" ie FB generation.One of my younger cousins actually said "didn't really happen till its on facebook!" at our wedding. She's a very sweet young lady - mostly a joke, I'm sure.
Not just a generational thing.
My now-husband and I got engaged in the evening. We had left Town A, where we were living, driven to Town B, he proposed, then we got in the car to travel to Town C to visit my parents for my birthday (I knew about everything except the stop-off at Town B and the proposal). So we were driving, at night, with very limited phone reception, and got in late.
The next morning his father posted on Facebook, before we'd had a chance to tell many people, "Don't forget to change your relationship status!"
On our honeymoon, my husband texted his parents a couple of updates from our trip. They posted the texts on Facebook, word for word. We flipped when we found out, and ordered them to delete the posts.
My opinion: how other people utilise social media should guide how you interact with them on social media. If they are private, respect that. If you visit their profile to congratulate them on news (engagement, birth, etc) and see no reference to it, sit on your damn hands.