Each of the proposed solutions are valid and each have their associated costs.
1) simply tell users they must use the 'www' record.
2) Install IIS on the DCs and redirect
3) Prevent the DCs from registering of the domain host records

All three are correct answers, when considering how to handle this issue. The solution that is actually implemented will depend on the organization. I can tell you certain factors such as user acceptance may rule out #1, security policies may rule out #2, and as Tiger indicated certain DFS and GPO operations may rule out #3, especially for those organizations that do not have alternate methods of name resolution, specifically NetBIOS where the domain name can be resolved using WINS 1C records.
Interflex, you should select one or more of the proposed solutions based on the business needs of the organziation.