As described in this article there is a strong need for fetch plans is JPA. Some people, even within the JPA expert group, seem to think there is no need for a specific API for fetch plans, they could be covered by criteria APIs. I personnaly think that a fetch plan is not a criteria or a filter, it is something related but different. Regarding this feature, data access technologies coming from the JDO world have some advantages, as this feature has been discussed with the JDO expert group since a long time.
Obviously, fetch plans are even more important when dealing with a disconnected data access model, like in Data Services. Some partial reconnection could be allowed when relationships are unknown during navigation, but current network technologies certainly cannot support full lazy loading over the Internet.