The "default players" are old Flash players, they are deprecated and should not be used. Their default playback method is progressive download, which is why they do not necessitate use the Nginx VOD module [which by default, listens on port 88 TCP, though as I explained, the port can be changed]. The default playback method for the HTML5 players is HLS and so, Nginx and its VOD module are needed for playback. If you prefer, you can use any external CDN that knows how to serve HLS manifests instead.
You can disable HLS playback when using the HTML5 player, which will make it revert to progressive playback but then, it will not work correctly on iOS devices and I wouldn't recommend that. Plus, for videos longer than just a few seconds, there are advantages to using an adaptive bitrate format [HLS, HDS, DASH] over progressive download.