I would say Twitter and Facebook in particular are still are incremental and trivial as billion dollar companies and always will be. The web is a dumbed down version of older hypertext systems and hasn't shaken that legacy in 25 years.
The real problem with the pace of innovation is these things weren't trivial to build, that's why the best we can do is incrementalism. And that comes from the foundation systems we use. When something near the bottom of a technology stack/pyramid offloads complexity to the top, it becomes a nightmare to get anything done.
For example, we don't have a natural language command line for regular/stupid users. Instead we have point and grunt GUIs. That means apps have to be monolithic. Apps can't work seamlessly with one another even if the underlying tech allows it.
And from that small bit of complexity we get billion dollar walled gardens.
More detailed read http://pchiusano.github.io/2013-05-22/future-of-software.htm...
Instead of a simple standard interface for users to access various services we have http://static3.businessinsider.com/image/4dd4d1cf4bd7c8c90f0... which kills discoverability and creates a constant drag on people to learn a million UIs. And then we hope to fix all that with another layer of AI http://whoo.ps/2015/02/23/futures-of-text
You can fool yourself about worse is better while making a few bucks. You can wall yourself off from the naysayers. But the real impact on the economy and humanity from eBay, AirBB and FaceTwitter is low.