That's a good question Dave. The main reason for native americans for using the gravity fitted hafts (without wedge) is that they were easier to replace when the haft broke.
A lot of people still does that and that's ok as far as you like the head fitted temporary. Also, this is better fitting regarding throwing. When there is no wedge, the powers influencing the haft after hitting the target are diverging evenly. This is different when you use wedge and have very tight fitting. However for using tomahawk as a tool, for cutting branches, making some fire in the wood, doing camping stuff - I personally prefer having my tool fitted tightly and don't bother with knocking repeatedly after use (in gravity fitting you need to hit the bottom in order to fit head more tightly). This is also cultural and historic aspect - slavic tribes, nordic ones used to use wedges
Hope this make any sense to you?