Some product people act like general managers, even owning profit and loss (P&L) for their product. Even if this is not your situation, executives and board members often want to understand business results and return on investment.
Business plan pro formas are not generally part of a roadmap, but adding rough revenues and a projected break-even timeframe can be useful to help this audience understand what you feel is required to reach a certain level of financial results. See Chapter 9 in my book Product Roadmaps Relaunched to learn more. Do you include financial data or other business objectives in your roadmaps? Tell me a story.