During a speech to investors, NVIDIA's boss Jenssen clearly stated that the world doesn't need a third CPU player:
I guess that he meant that the other two are Intel and AMD, as we know that VIA, Transmeta and IBM also make CPUs that can power computers.
Jensen also said that even with Nvidia's Tesla graphics card, that can calculate big streams of data, you still need a CPU and that CPU is one of the best engineered microprocessors in the world. It is programmable and it took Nvidia years until it moved into that space.
Today with G80, Nvidia's graphic chip can almost do all the tasks that a CPU can do, so there is only a thin line between the two.