Wikipedia already has a book lookup feature that gives the user the option to look up books using the ISBN.
This even works for the Da Vinci Code, so I can totally see why an individual link to worldcat on a book record might be viewed as a not good way forward if there is already a process in place to look up books in WorldCat, RedLightGreen, and online booksellers. I really wonder if this room full of outraged librarians knows about this tool.
Why not work with wikipedia on their existing form for looking up books?
Update: It looks like the editor who removed the link clarified the answer. One thing that might be useful when asking editors at Wikipedia questions about policy is to sign up for a Wikipedia account yourself. I imagine that wikipedia users might be more likely to answer questions quickly when they come from other members of the community.