Let Your Friends Know???

I guess this minor incident is considered ubiquitous by most, but for IcyJane in the cold Northern Woods, it was something new....
After completing a recent online purchase for Nutcracker tickets, a happy message popped on the screen. "Now that you made this purchase--let all your friends know! Share on Facebook or Tweet!"
Why? Oh Why should I?? Not that the Nutcracker is an everyday event, but why would I bother my "friends" with this information??
Does everyone these days have really lame friends? Who wants to know this information? If you are going to the Nutcracker--good for you, but I don't want to know. And please don't contact me about it.
I understand it is a marketing trick--"IcyJane is going to the Nutcracker--so should you." But if you are going, just because I am (and not by your own interest) then you are too unoriginal to be my friend, and I would unfriend you anyway. Obviously I do not understand social networking...