When I first started working on Forge I thought that it shouldn't have any "bad cards" because no one would use them. But after thinking about it, I decided that Forge should have every Magic card that it could support.
I thought that I could easily classify cards as good and bad but the lines get fuzzy very quickly. Sometimes a mediocre card might be good in a tribal deck or maybe that card is pretty good in one of Forge's "limited modes" like sealed, draft, or quest. If you are using all of the cards you probably wouldn't include many 3 mana creatures that are only 2/2 but they make up the backbone of most limited decks.
Winding Wurm is a good example. He is a 6/6 creature that costs 4G but also has an echo cost of 4G. (Echo means that you have to play 4G again on your next turn, so the total cost is 8GG.) Back in the day this card might have been used in a constructed deck but without trample he is a little weak. I happen to get him during a quest and he was amazing. Even though he didn't have any other abilities, he was a one man Godzilla. Winding Wurm is mediocre is some formats and exceptional in others.
This is also a good example of why I don't think Forge is costing Wizards any money. Most of the cards in Forge are not in print. Also, Forge enables players to use fascinating cards from Magic's long history like Winding Wurm, Ali from Cairo, and Skullclamp.
I wanted to write an April Fool's column like, "Wizards is going to buy Forge" or "I got hired by Wizards" but I didn't want to be too stupid.