Let me preface this by saying that I am not an Intellectual Property lawyer, and most of my IP knowledge is from back in '94 when I was in lawschool, ranting and raving against TSR on Usenet. So don't anyone take this as legal advice, please.
Also, I barely know 4e, I don't know what Powers and Power Cards are, and most importantly, I never saw the site in question.
Now that it's been established that I have absolutely no basis for a legal opinion of any kind on the matter, here's my personal non-lawyerish opinion.
It sounds like the guy had copyrighted material on the site, and WOTC had a right to take it down.
It seems like, according to Scott R., someone could put up a power card with fan designed material in it on a website. Since a Power seems to be a new part of 4e, able to be licensed under the GSL, then under the current GSL, as I understand it, that right to publish it can be taken away on a whim. It also seems that in the absence of a fansite policy, in order to protect your ass when it comes to publishing a Power Card on your webpage using the template, you may need to sign the GSL. That seems to be the cautionary implication I get from Scott R.'s posts in this thread.
Since there is no fansite policy in place, I would suggest everyone take the recent C&D letters as a warning. Though the material in question in these last couple enforcement actions seems to have been wrongfully published, in that copyrighted material was published, in one case for money and in one case for free, it is an indication that WOTC is not messing around when it comes to perceived copyright violations.
Can a person put up something vaguely in the shape of a Power Card and call it something else, and post what are essentially powers on the card? Yes. Will WOTC try to do something about it? Who knows. You can be fairly certain that if they do, they'll threaten the hosting company, and the company will shut the site down if the owner of the site doesn't.
That's just the way it works. I have found that the law is usually less about what is legal, and more about those with power doing what they like through the law against those without power.
No one wants the hassle and expense of a lawsuit. I've done stuff like what WOTC is doing myself. A client of mine had a book published which had what could be considered defamatory comments on a website about the book and author, beyond just your typical "this book sucked." So I sent them a "I JoetheLawyer will sue your ass in Federal Court unless you take down all bad comments about this book" letter, and within a week the offending comments were removed. The website was Amazon.com. They had the power and money to fight i if they so choset. Most small website hosting companies don't. What do you think the small companies will do? The same thing they did in the early 90's when TSR started their clampdown.
My opinion, as I have been stating for months now, is that one of the motivations for such a radical change from 3.x to 4e in terms of terminology was so that WOTC could do just this: Clamp down on anything which in their opinion may cut into their sales. They wanted to undo the
OGL as much as they possibly could. Hence Powers, Bloodied, and all the other new terminology and changes which seem to be changes mostly for the sake of the change. They want to take back more of the market.
Call me cynical, but I don't think the ridiculous delay of the revised GSL was unintentional either. It's just good business to do so. Bad PR, but they may be of the opinion that they can spin that bad PR away.
I do remember Scott R. saying recently in a post that he was investigating websites for IP violations. I thnk that post was in response to a "Where's the new GSL?" post. I think that's a fairly good indication of where WOTC's priorities are these days, and perhaps a glimpse into the future. We'll see in a few years where we're at.
I don't blame Necro Games and others for taking a cautionary approach to publishing for 4e. Who knows, the revised GSL may adress their concerns. Judging by how long it is taking to get revised GSL though, I wouldn't hold my breath waiting for a fansite policy.
Anyhow, I'm typed out on the matter. All I have to say is thank god for Pathfinder and all the other OGL-based games out there. Because of the OGL we will never be in a situation many of us remember from the early 90's with TSR.
Since I don't like 4e anyhow, call me self-centered, but I don't give a damn what WOTC does these days. As far as I see it, these sorts of aggressive enforcement tactics, delays in licenses, and bad PR moves all push gamers away from 4e and into systems that I play, increasing the relative power and marketshare of those game systems and their players.