I don't really know what I would consider to be the definition of a true walker, but I've always classed Anarchy as a walker in my mind. Even when the rules were changed so that it was classed as a shuffler, I never thought of it as that. The problem with that I guess, is that people will find ways to replicate Anarchy's leg mechanisms without using much weight and will then be able to fit much heavier weapons systems on to their double-the-weight-limit robots which in turn may prompt other people to complain about the classification of a walker.

But then this is just my opinion. I think it's difficult to fully classify as well. For example, I consider Clawed Hopper to NOT be a walker, but I believe that is similar to the mechanism used in DrillZilla (except more precise and much faster) which I originally DID class as a walker. So a lot of it could come down to personal opinion.

The best example of a walker that I can think of is Junior, built by the Plunderbird boys for Technogames. A lovely little machine to watch in action, and that is something I would definitely consider a walker.

Sorry, I know that's probably not much help :P