do the same thing—they decide how much they can do by the sprint end date and commit to that. Commit a little, accomplish a little. Then, they whittle away at the overall goal for the release end date by making smaller goals within the sprints.
Yes, it does happen that the team accomplishes less than it originally committed to for the release. But, ask almost any businessperson in almost any situation "Which would you rather have, all the features delivered late or most of the features delivered on time?" The businessperson will choose the second option most of the time. Business runs on budgets and dates. The people most concerned about the exact feature set are usually the technical people. Of course, businesspeople will insist "I want all those features delivered by this date and within this budget!" But, you know what that's called? It's called negotiation. Make your initial demands and then see what the other guy does. Trouble is, most of us technical people are terrible negotiators. So we give in too often.
The agile question "How much can you do by this date?" is the better question. It does involve a certain level of trust of your project team. But, it provides a better resolution of what "it" is, without assuming anything up front and by exploring "it" until "it" comes together at release time. And, the agile question also provides much better value to the business, by playing on its terms of fixed schedule and budget with a flexible set of features.