Wikipedia's entry on WGS 84 indicates that the most widely used global reference frame is only valid through 2010, but it doesn't say why.
The World Geodetic System defines a fixed global reference frame for the Earth, for use in geodesy and navigation. The latest revision is WGS 84 dating from 1984, which will be valid up to about 2010.
Does anyone know if this is correct, and if so, why?
I don't know for sure, but I would suspect that there are two factors involved:
First, the shape and density of the Earth may change slightly over time.
Second, the many contractors involved in monitoring the shape and density of the Earth would like to ensure their future funding.