Brain, this is a great question and "one for the ages" as it is a question that has been continuously raised during the 4 decades that I have worked in product management. One of the reasons there has never been a clear answer regarding where PM reports, is as Jennifer points out, "it depends". Some of the primary determinants are corporate culture, size, structure, and level of maturity.
First for contextual framing, consider the foundation innovation elements of "what" and "how". The "what" is primarily focused on defining the value proposition with consideration of market sizing, competitive positioning, pricing, channel design, market trends, fit to corporate strategy, and fit to business model. These are classic product management concerns. The "how" is focused on developing a solution to the defined need, including consideration of manufacturing costs, support costs, overall development costs, material science and other technical trends and techniques. These are classic development concerns. You need both sides for successful innovation, and as Nicholas points out, the scope of skills required are quite broad.
Most people get these activities are different functions, and the question is where should these functions sit in an organization?
This gets back to the "depends". If the company culture and state of maturity is such that the marketing organization is solely focused on "here and now" activities of sales support and lead generation, then product management is better served by sitting on the development side of the house. However, this means the development organization then owns everything from idea generation and selection, through product launch, including creating of launch material, collateral, pricing, establishment of key channel partnerships, and the activities needed to transfer the knowledge to sales, partners, and support organizations. This is not something many development organizations want to particularly own.
What I have seen to be quite common in mid-size technology firms, is that product management is a separate functional area that reports into either the CIO/CTO, or the CMO, and in some cases the president. In either case, even when reporting to the CIO/CTO, they aren't part of the development organization, they just share the same executive leadership. The specific reporting structure is based on the prior comments about the domain scope of the senior executive involved.
The often touted phrase "the Product Manager is CEO of their product line", is more about the fact that in either structure, it is the responsibly of the product manager to pull together all of the various cross-functional elements needed to make the product successful, as referenced in Pat's comments. Just like a CEO must pull together all functional areas. It is less about ownership of P&L. In my experience, by the time a PM's career advances to the point of P&L ownership, they are no longer a PM, but have a title like Director or VP with product managers on their staff.
When appropriately defined and supported by the organization, the reporting structure doesn't matter. Where I have seen organizations get into trouble is when the technical lead of CTO/CIO owns the product management function but doesn't accept ownership of product launch and market success, or when the CMO owns product management, and buries them in lead generation and sales support.------------------------------