Facebook | Application is no longer available on TVs LG SmartTV, because Facebook ceased to support and develop API for Smart platform on April 30, 2015. Without support of the manufacturer's application, its main functions stopped working. You can still use Facebook on a web browser.
Spotify | Application is available for download by LG SmartTV Store on models with WebOS and WebOS 2.0.
Twitter, Skype | Applications were withdrawn because of the difficulty in adapting them to Smart platform and their limited performance. Currently, there is no possibility of using Skype on TVs LG system WebOS, and WebOS 2.0. You can still use Twitter on a web browser.
I received this information in correspondence with representative LG Electronics Poland. As you can see, LG is not directly responsible for the lack of these apps on webOS.
So we're sorry LG and many thanks for your answers. Now we can wait or go to store to buy another TV.