You have absolutely NO IDEA how many people absolutely do not Tweet- Twitter- or anything else remotely like that. Lots of us never do Facebook because of the incredibly high amount of personal information goes awry.
Some of us actually have conversations face to face!!!
Have to admit, I have been thinking of closing my fb acct for that very reason. It was interesting at first having old friends on my friends list I hadnt seen in 25 years, but honestly how well do they know you if you havent seen them for that long? What reason is there to keep the acct if you would gain more by talking to them over the phone, or face to face?