-Yeah, HTML5 probably plays a big role in this.
-If you feel that default is good, that's fine. Every game where it makes sense to have remapping should have it though.
-The way I did join up might not work for your game, but if you think it does, go for it!
-With the Sonic Spider thing, that control style is pros and cons. You will never be able to make it feel right to everyone, so follow your heart.