The truth is (as usually) not nearly as simple.
There are different styles of writing and different audiences you're aiming at, but not only the split doesn't go along the line of "online/offline", the line is not nearly as clear-cut as you're trying to make it.
Some of the longest books even written never reach paper and have avid audience online. And paper newspapers are still common, many of them keeping quite condensed formula.
And speaking from my experience, while I tend to prefer bite-sized pieces of data that happen on blogs or online news sites, plus love to write small articles or read blogs, whenever I'm not writing something lengthy, I'm reading something lengthy. I belong to both audiences at once.
And it doesn't matter if I'm reading Master and Margarita in paperback, or Fallout: Equestria in Google Docs, they are both novels of considerable size. Doesn't matter if I read the free newspaper, Metro, while going by public transport, or skip to Tumblr to see my favorite blogs with my smartphone, I read snippets.
Not to mention both formats exist for ages. Contrast Aesop's tales vs the Illiad. In young people's busy lives "snippets" became more popular because they don't need to sacrifice so much time to absorb them, and elder people with slower lives and less prone to use modern tech may prefer to spend time with a traditional book.
The divide you may be observing is not related to medium, it is related to preferences of the audience: early adopters with fast lives and little time prefer electronics and prefer short. Calm conservatists with lots of time and taste for quality prefer traditional media and long content. Medium changes, and proportions change - but both formats exist and both exist in all media there are.