Thanks to all for their comments so far! Let me address a couple of points:
Chris - I agree that placing the clustered index on the identity col itself won't render great gains. Remember, I didn't say that was a best practice, just a better than nothing practice. Having a clustered index anywhere in the table affects how other indexes are built/used, I believe better to have one than not. Sure it would be better used on a "perfect" key - but if they could do that, they wouldn't be in the WP category to start with! I'll have to think in your fkey argument - hard for me to disagree, but should it be a worst practice?
Dood - I addressed this to some extent in the article. Indexes arent always about speed, but data integrity (as constraints). Putting the index in place is also good planning for future growth. Aside from a primary key though, additional indexes should be used as needed only. If you KNOW it'll always be a 50 row state lookup table (or 51, or 52), then I'd agree no additional indexes required.
Andy - Hey, I hear you man - if you've got a good candidate key, use it! My goal is to get people thinking about the worst thing they can do. If all your developers build tables that always have a primarykey and always have a clustered index they've at least taken a step in the right direction. My hope would be that no table gets deployed without a DBA reviewing first - that's a great time to do some mentoring if they've created a fake pkey when a real one exists. One day we'll have to tackle the identity col issue just for fun!
Skelband - I agree a bad clustered index will cause you problems. Identity will never be one of those though. It's an "ok" plan at best, just better than nothing. For the second part, I agree - though in practice there is nothing that says you or your app can't be responsible for maintaining uniqueness rather than the db.
To everyone: The tough part about these articles is that identitying a worst practice gets you thinking about good, better, best practices. My thought was to present at least "ok" alternatives that a user could implement without a lot of work or knowledge. Is that going to do more harm than good? Leave that for the ensuing discussion? If you gave this to a new/junior programmer to read one week for professional development, would you/they be better off for having read it? Would they learn one bad habit to replace another?