IPFS "servers" are called peers. DTube is just a window to data. When people uploads a video to DTube, what it is happening in reality is that DTube adds the video to their own peer. Every user which adds that file to their own peer will make the download much faster.

So, a very quick way of uploading a file to DTube is adding it to your own peer and telling DTube the hash of the file, instead of uploading it. Then the content is available directly, while DTube itself will add it to their own peer.

It is very likely that DLive and DSound are making the same..

Busy, for example, is now uploading pictures to IPFS instead of using a common server like AWS.