How is FB spelling doom for TWTR? They aren't exactly competition. Let me ask you something. Do you know anyone who uses ONLY Facebook? A user of facebook most likely has other social media accounts with twitter, instagram, g+...
You are acting like it's some kind of consumer good where u either buy and iPhone or Android. This is social media, where it's about sharing ironically.
Oh and I suppose FB never stole from anybody(winklevoss).
It can't be a killer when it's not the same thing. Instagram is primarily for photos. You can't post a random thought unless you take a picture or link to another website or news story, unless you post a picture. Twitter, you can do all the above as well as posting a pic or video too.
I don't think a recent self survey counts as a real survey.