Sorry, you guys can disagree with it, but its how people think.
Lets say you give me 5 things for $40, and I'm happy. Great.
Now give me 10 things for $40, but I don't want 5 of them. Now I'm unhappy. I feel like I got $20 worth of stuff, and was forced to pay extra for things I don't want. You ruined the deal.
This is how consumer expectations work. There's tons of ways you've seen these things happen. When a company announces that a product will be released in June, and it is, you're happy. When they announce it will be released in May, but they run a month behind and give it to you in June, you're unhappy. Even though you got the same thing!
The way you offer products crafts people's expectations about the products you offer. I think that including with every book the option to spend extra money to use the book in a particular way makes people feel like you're charging them for the book they already own. Even though previously they weren't able to use the book in that way at all, so really you're offering them something extra for extra money, you've shaped their expectations in such a way that they expect more for the same money.
As for including home brew in online play, they can't include all types of homebrew. If they did, you wouldn't need access codes at all. You could just enter in a real book as an alleged "homebrew" entry.