- They are relevant to the requirements for a product.
- They are part of strategic product management.
As your product manager is understanding the problems in the market, the distinctive competence of the company, and the competition, she should be formulating the positioning of the product using established positioning principles.
Branding strategy and positioning should in fact drive product requirements. Should your focus be on ease of use, customizability, or style? The answer to these sorts of positioning questions determine which problems you choose to solve and thus what the requirements for the product are. They also determine how to prioritize those requirements.
A strategic product manager is a product manager who sets the strategy for building and marketing the product but doesn't necessarily do a lot of tactical outbound marketing (e.g. writing white papers, creating brochures, etc.). Positioning in many respects is a less tactical activity than specifying product requirements, because it sets the vision for the product into which the requirements must fit.