1) lead manufacturers claim that concave studs are supposed to stay sharp longer so these days most "pointy" studs are cheap with steel body
2) homemade studded tires maybe work better on pure ice but very slow
3) narrow tires (2.1-2.3) with studs much faster and more fun to ride on ice
4) agree with the previous post, you really need only central studs unless you want to ride 6 Mile Run in very icy conditions