Now you are talking damages again. You could still smack them (i.e. ABC Roleplaying Co) for the crime of copyright infringement.
You might not get any money from ABC RP Co, but you can certainly stop them from doing that.
The only price that can be paid for copyright infringement is a set of damages.
So if ABC is ruled to be doing zero damage, there is no price to pay for the infringement and it can continue in perpetuity as it is doing no damage.
Now, web site "A" who is offering a free service can be demosntrated to be doing damage. Every time somebody uses the service, that's a DDI subscription of a Power Cards sale that WotC does not realize because the end product was delivered by web site A.
So if it can be demonstrated from web logs that web site "A" had 9000 individual PDFs created, WotC wouldl be within their rights to demand $45,000 in damages (9,000 times $5/month DDI subscription).
Failure to enforce the copyright immediately would decrease the value of the copyright by $45,000.
Now think about it. You're Gamer Goodguy who created web site "A" out of the goodness of your heart and your love of the game, but when you realize you could be liable for $45,000 in damages your web site did to WotC, plus any potential punitive damages and court costs, what would be your course of action when you receive the C&D?
edited to add: Also, if Gamer Goodguy says, "NO" to the C&D, WotC then sends a C&D to hosting company "A" who then takes down the site. Hosting Company "A" won't risk being held liable for this blatant violation of WotC's copyright.