The amount of computing resources put into place with a grid architecture can be enormous. Companies get to add the equivalent of a couple thousands PCs and that added horsepower that they do not have to pay for.
Two- or four-processor computing is the typical entry point in lieu of grid computing. If it works on inexpensive servers, then good for you.
A lot of these high-end business applications have a very high return on their investments. With grid architecture you can be ready to do that.
This is a more shrink-wrapped approach for the concept of grid computing that targets a more modest area of use.
Sun Grid is pretty much a laughingstock, because they announced it multiple times and they failed multiple times to deliver it.