There is value in having a shippable product because it implies that the product quality has been kept higher than it would be if development was performed with a longer term shipping plan.
One has to keep in mind the motivation for the "shippable" requirement. In many software projects with a long development schedule, a lot of resources might go into developing one portion of the software, usually the area called "essential infrastructure" when communicating with higher level managers. This may lead to an imbalance whereby too much resources are spent on one area, while other areas, such as testing, or UI design, are starved of resources. In the end, resources may run out, and the end result is an unusable product.
If on the other hand, the product is kept "shippable", the project at least feels like it was not a complete waste, even if the plug is pulled on development mid-way.