Social media like i.e. Facebook is mostly a place for narcissism, networking or voyeurism of various forms.
It can also be seen as a a lazy persons contact list, or as a place to waste huge amounts of time playing with various applications.
In other words, they are not really that social like the name suggests.
However on your birthday the social interactions seems to flourish. People suddenly decide to use the media to be social, A simple click and a (true) heartfelt message later, and you have done a truly social act.
You have made someone feel special and thought of, although everyone involved really knows it is due to the reminder in the corner. But that doesn't matter, a well wishing, is always a well wishing, electronically reminded or not.
So, for all of you who uses social media to congratulate me, thank you very much, it warms my heart, and expect the same in return, when I see your name under birthdays today. as this is a good excuse to socially interact via social media.