I totally agree with this.
There is no bigger disservice to your team or company than being the guy in charge whose knowledge is 10 years out of date.
That doesn't just apply to technical things either. It's an easy example to talk about the project manager who cut his teeth writing procedural code in QBASIC and has an unrealistic grounding. It also applies to the store manager in a fast food restaurant who hasn't made a cheeseburger.
I think those are two different jobs. On one hand you have the Product Leader, whose job it is to stay on top of the technology that drives the product, and to be aware of the codebase. On the other hand, you have the Team Leader, whose job it is to facilitate communication between team members. To make sure team members are productive and happy.
That doesn't just apply to technical things either. It's an easy example to talk about the project manager who cut his teeth writing procedural code in QBASIC and has an unrealistic grounding. It also applies to the store manager in a fast food restaurant who hasn't made a cheeseburger.