It's all about the money. If you want mobile, you have to pay for it. If you want the the screen to come to you so that you don't have to go to the screen, you have to pay for it. If you want to use all the features of Mendeley/Ning/Sliseshare, you have to pay for it. If you want to sell content online, you need a new platform people have not come to expect as free.
Which raises an interesting point. With the long tail, monetisation was straightforward. All you had to do was to ride on the coat tails of a big provider - the bigger the better, and they didn't come any bigger than Google. In this brave new world, how do I monetise me - my knowledge, expertise, filtering? Is there an app for that? And if there was, would people pay for it?