I will start with the joel case then go in general.
First, he did nothing illegal because every single information was there from day one. The whole problem was the way to deliver this information.
When you come across the sale page you expect to buy a book. Then you scroll down and you see a free gift area. Usually , you don’t expect to see an important note in a free gift area. In anybody head when it is free it is free. It like me doing a contest and giving you a car with a fine print telling you I only buy the fist month and you have to deal with the rest.( come on )
This is the way the sale page was build.(now he change it )
I read everything. Until there I was still thinking he was giving away a first month and then you will have to subscribe for the newsletter.( and it was an automatic opt in)
When I click the order button .. I saw that I would ordering two products.. The only ways to take it off was waiting for the newsletter and then opt out several days after ordering.
( people are saying that even after check out .. he was still trying to sell other product before you get the confirmation page.. I saw a lot of marketer doing that just make sure then can get every penny from the customer)
There is nothing to do about how long the sale page is. If you are buying for one product it is all good .. they can put as much testimonial as they want …
here the presentation was mixing two product in one ( every affiliates didn’t even know about the newsletter)

I do not see a mistake but a marketing strategy 101
I have no idea how the book is build but a good strategy will be to finish the book by saying Google Adsense change all the time so stay update keep in touch with my Adsense club (newsletter)

Again I have no idea how the newsletter is build but another strategy is giving a preview about what’s going to be the second edition (where he will get the 30$)

10$ is a publicity stunt because the whole deal is the newsletter!! ( this is where the real money can be done)

It is not really about if the product is a scam or not but the presentation.

Why he did an automatic opt in ? most of the people will want to see at least second and third edition before opt out.
If will ask in another e-mail to order the newsletter ( 90% won’t subscribe for many reason .. lazy feeling cheap that day etc…)
Is it legal ? yes is it ethical? Not .. as simple as that.
In a moral world.. You should be able to opt out on the order form….

All this remind me my ethical course.. how far you should go in marketing.
Yes sale pages work since day one like info commercial but where is the limit between a good marketing and a bad one.
That money justifies every thing.
I still thing a good straight and clear campaign is better.
A great example is the problogger book. No gimmick no 40 useless testimonial
He just give away the first chapter.. this is the most effective way to do it. Sample is by far the best promoting system.
Another great sale page I saw…where I think people should do more like this.
You sell product explain your product and give away a free video tutorial to show your product in action on your sales page…
This is straight marketing like the money back guaranteed format( where we all know only 5% of the people who don’t like the product use it )

Wow I talk a lot ahaha maybe time you put video comment like techcrunch (wink wink)
Ps: Have you read the book?