I agree with Kenocide's points above. Personally I think relationships should be quite private. Not hidden away, but just between two people and not something you go on about, especially in front of people that are single.
But I do think it is sometimes driven by insecurity, when people have to always be publicising either in person or on facebook/twitter the fact that they have a partner and telling everyone what fun activities they are doing together, it is all about painting the image of their perfect lives to convince themselves as well as others.
I remember my last girlfriend, when we first met and I added her on facebook there were loads of pictures of her with her ex boyfriend who she had been seeing for about 2 years, and I felt quite jealous when I face-stalked her, even though I was with her at this point in time, just seeing how she was always posting love hearts beneath every picture of them together and making comments about how in love they were. But as I got to know her more and she told me about her last relationship, it was clear that they had been having massive problems for a long time, and some of the time she was doing all this lovey dovey stuff on facebook they were not even talking to each other. I brought up her facebook interactions with him to her when she was telling me this, and she said "yeah, I think I was just trying so hard to convince myself, as well as other people, that I was in this perfect relationship really". So fair enough. But I bet she irritated the crap out of other people with that kind of thing. She didn't do it with me fortunately.