In many projects there is a lack of trust between the business and the development project. The business has seen too many projects that are late and deliver the wrong product. By using the first releases to deliver value to the business the project can build trust that will be essential later when Pain may be necessary. Another way of building trust is to use Limited releases. Even if you feel confident that your project will deliver releases of high quality there is always the risk that there are business requirements that have been overlooked or misunderstood.
When the business has trust in the project it will be much more willing to accept that some features must wait until a later release.
Chris Stevenson and Andy Pols discuss the value of building trust in this excellent case study: http://skizz.biz/blog/an-agile-approach-to-a-legacy-system/. (One thing to note though is that when they talk about a test release they are actually talking about a Limited release).