I am much the same way with my music collection. I have my music sitting on a NAS which my Sonos devices can access. But on the other hand I am also a fan of services such as Spotify and Pandora. I love my Pandora radio stations and I have many Spotify playlists for when I go to the gym. I love that I can access all of my different music sources using the Sonos app and play it in any room of my house.
Sonos is a bit like Apple where they get hardcore fanatics that love their products. I guess I fit that bill (love Apple too!). Sonos has to be the best tech purchase I have ever made (this includes my iPhone 5s, iPad Air and Macbook

). It has changed the way I listen to music and I listen to it more than ever thanks to Sonos because it makes accessing it so much easier!
Some people are a bit different to me and seem to be exclusively using a single app/service such as Spotify, Rdio or Google Play Music. They use this app in the car and at the gym etc therefore it is probably a pain for them to have to switch to the Sonos app to continue listening when at home. Sonos is now working to allow everybody to use their favourite app and still stream it through Sonos. Think of it like the Apple TV which has integrated with Netflix and Hulu Plus etc. Instead of having to use the Apple TV interface, imagine also being able to use the Netflix app on your iPhone or iPad and then casting it to Apple TV. Lots of different options for searching and selecting content.
I'm not sure where you are getting the idea that Sonos is promoting a media server. They have made a great music system which they have partnered with all of the major players to access their content. Now, they have just made their product even easier to use.