For the average person posting a pic on Facebook, using their smartphone camera might have more benefits that outweigh good photo quality of a point and shoot. On a smartphone, you can do basic photo editing, post directly to social sites without having to transfer pics to your computer (I think only some higher end point and shoot cameras have that function), and you have your phone with you all the time anyway so a camera is readily accessible.
Besides, the photo quality of the iPhone isn't that bad... all these pics are taken with an iPhone 4s:
