I wonder if Internet speed and mobile Internet also plays a role.
For example, if I want to listen to a particular song on demand, I go to YouTube, look up the title and click the result. If I'm not interested in watching the video, I just minimise the browser (or switch tab). Same goes with on the move - YouTube App, assuming I'm in an area with 3G coverage. Most of the time, I just listen to FM, DAB or Internet radio, as there are very few recently released songs that I would be interested in listening to on demand.
However, in many countries where iTunes and Spotify are not available, there is generally much tighter Internet caps and worse mobile data coverage & charges. Assuming an Internet connection is quick enough to watch something on YouTube, the data usage would quickly eat up one's monthly allowance, especially if they listen to multiple songs a day. MP3 downloads on the other hand take far less bandwidth, even if they end up being uploaded multiple times through BitTorrent sharing.
As for listening to music on the move, those in poorer countries either don't have handsets capable of watching YouTube and those that do probably could not afford the data usage, so the main alternative would be to download the songs before heading out.