[Geee]

The point is that the information about the book might not be completely objective when money is involved. It's that tiny bit of bias that might get injected in the article, by someone who is affiliated, be it Amazon employee or someone from Wikimedia. When this might not be a real issue, no one can be sure, and the trust in absolute objectivity is lost.

[JustinSeriously]

You're right, but money already is involved in these articles. Authors and actors (and agents, I've suspected in a few cases) are keeping a biased eye on their articles.

I think it would be difficult for Wikipedia to be corrupted by money. There's too much transparency, and there's too large of a community. The admins have already discovered with dealt with large-scale attempts to game the system.

What's actually at stake here is the appearance of objectivity. Affiliate links, which are nearly universal across the web, should be minimally objectionable.