Bill, I believe that Information Architecture is the only true path that guides a user thru the experience of using a product. Obviously, graphics, colors, etc. play a role but they are always secondary.
For example, you launch an app and the very first screen sends you a very specific message based on all of the information on it and how this information is architected into the UI. This same information takes you all the way to the completion of your task (the goal of using this particular product). This IA guidance is what enables the user to ultimately derive value from using the product as they experience it end to end (while being guided by the information). For example, if IA is poorly designed, then the derived value is low. So, for product managers it’s critical to have a good understanding of Information Architecture because if they don’t know why users end up being guided into low product experience value and how it can be fixed, they will eventually run this product into the ground which directly translates into product management fiasco.
Hope this high level mumbling helps! :) Feel free to ask more specific questions based on the above if you have any.
Have a great weekend sir!