I do not understand the paragraph,

"Every IT professional has banged up against the sponsor who, at every juncture, wants to remind us that you said it would cost X!. Now we set up the relationship that that the sponsor is telling us the number they imagine. Theres no guarantee we can deliver within that investment or timeframe, but we can make sure the sponsor understands that business case justification is their job, and ours is to apply the expertise and creativity to deliver the results."

This makes it sound like representatives of the sponsor are not on the Agile team right from the start. If representatives of the sponsor were on the team right from the start, wouldn't that help ensure that the roadmap is being driven both by business requirements as well as by what the agile team thinks makes sense over time? I must be missing something here.