For every kind of Web site, the user wants to accomplish something. In contrast, on an entertainment Web site it is rare that users have such specific tasks. It is advisable to determine what the common tasks are that your users probably will want to accomplish, so you can support them better with your site's content. The classic rule is to test with people from your target audience, not just with people you happen to know, or with people selected at random. I'm not saying that an editor couldn't learn information architecture skills, but in principle I believe they are two distinct roles.
Information architects look at structuring a huge amount of information.
Also, the methods used by information architects are quite different from editors' methods. For example, information architecture is where you do more usability testing and modeling. I've just been converted into believing that content is a hugely important issue, so I'm definitely discussing it in my book. You need to be aware of more than your narrow skill set. This book covers all of the issues in Web design, and shows how they're related.