This is really a good question and it made me think. Why exactly do we use a block versus an anvil when making jewelry?
This reader mentions working with wire but shes not real specific about what she does with it, so one thing to ask yourself is what do I want to do with my wire? Do I want to work harden it (stiffening or hardening metal by bending, hammering, or stretching it)? Do I want to shape it? Do I just want to bang the crap out of it?
Normally, an anvil is used if you want to do some major hammering on metal and also if you want to shape parts of the metal. This is especially true with metal plate jewelry pieces, such as my cuff bracelet project. If you look at most anvils, in addition to a surface area for hammering, they have protruding areas, called horns, that allow you to shape metal around.
A bench block, on the other hand, is just that a block o metal. This is good for pounding and hardening, but theres no place to shape. In the book Bead on a Wire, Sharilyn Miller talks about blocks and uses them in many of her wire jewelry projects.