Roman Pichler writes a great article, Product Manager vs. Product Owner.
I've always thought of the product owner role as a subset of the product manager role, and that still rings true for me.
When companies do not have a traditional product management group and they begin using Scrum, the product owner role jump-starts agile and acts as a bridge to product management. That's a benefit I've never heard before. A brilliant insight by Roman.
He suggests moving past the product-manager-product-owner debate by simply talking about product people.