The graphic may be true when comming from an occupation which always produces written content.

But regarding myself (and many other bloggers), "Blogging" is not decresing the volume of written content. That is because I (we) would not write at all if we did not blog.

Well, maybe we would, but not as much and only for ourselves. So I think that "Blogging" in fact does increase the volume of written content.

The question is: Do authors who would have written high-quality blog articles increasingly jump to more volatile platforms, e.g. microblogging.

(Btw.: I don't like the term "microblogging" for Twitter either, as Twitter is more about short messaging as it is about crafting real content.)

It's not a problem per se we produce less written content. You don't have to be verbose to be deep.

The problem is we produce more superficial content. Make something easy to use and mostly fools will use it.

A longer than 140 character blog entry needs at least some thinking and time to compose. With Twitter there is no such constraint, therefore it obviously has less quality content, because it requires less thinking.

Retweeting is the new trend ! ..