I think your missing the point. SMPEG is a library with a player "plaympeg" which just demonstrates the use of that library and isn't meant to be a fully featured mpeg player. SDL and SMPEG are commonly used on LINUX to make all sorts of cool stuff. plaympeg is just a concept player.
Look at this as a good thing. Linux enjoys inovation by Open Source programers using such libries and the amiga can now enjoy more of the same. :-)