I think the fear most product managers have is that if they connect one customer to a developer, that developer will take that one customer's needs as the requirements. The problem, of course, is that one customer is not representative of the entire user base. This is probably an underestimation of the developers, who are perfectly capable of distinguishing the forest from the trees.

Too often, the only interaction developers have with customers is when problems arise. This kind of interaction doesn't provide much insight into customer needs. Instead, you sometimes need to have higher-level discussions to understand why customers need the features you're developing and how do they use your software to solve problems so that you can develop a better product. It's the developers' job to get this message across to the product managers, who should then be happy to step out of the way.

I think it's also important for developers to take an active role in learning about *all* their users, as a group, on their own time. You can look for online communities or attend trade shows and meet people face-to-face. We've also had some success by asking for contact info of some customers from the product manager and scheduling phone calls to discuss the customer's experience. In other words, don't wait for the product manager to do this for you, just do it yourself.