Read my Tweets!
Why? That's a good question, and one to which I have no definitive answer.
It seems to me that blogging and tweeting are very much the same thing, casting your thoughts to the wind for no other reason than that you can.
Maybe, just maybe such exercise, being one that requires thought and some degree of manual dexterity (just to type) will contribute to the well being of participents. There was an article on Today on Radio 4 earlier in the week describing a study into dementia which suggests that keeping an active intellectual life reduces the risk factors for the onset of Alzheimer's. Perhaps there's a study to be done correlating numbers of bloggers and tweeters with dementia sufferers?