You're a product manager in charge of developing a new product, and you've done months of research to determine a direction and a vision for the product. The product development is going well, and now you've involved other departments, like marketing, graphics design, sales, and operations in order to create a support chain for the product.
As more managers of these areas get involved, many of them will have their own views regarding how things should function. For instance, you, as a technical person, may picture the development team implementing a new architecture that uses web services to bring custom API's to your clients and internal developers, which will help the other developers extend your product by using the services it provides. However, the marketing and operations personnel may view the architecture change as unimportant as they don't have the technical knowledge to understand how the new architecture could power other products built using that technology.
What you want is similar to what marketing and operations wants, but since they don't understand software engineering, they may not understand what the developers are working on. They then use their influence to convince others in the organization to skip the architecture development.
While it may be beneficial to include department managers in meetings -- instead of just the resources they've allocated to your team -- sometimes it's more difficult to control the direction of your product in these cases.
What tips or suggestions are out there for gaining support from other managers without necessarily having them take over the project with their influence?