No exclusives would mean there would be no point in owning one console over another. Some people really do just buy one every 4-5 years. The various console "wars" over the decades have been beneficial to the growth of the industry and the development of original software, not a hindrance. You need standardized, easy to use hardware so that developers have a well-defined set of hardware limits to work within and owners all have a similar gaming experience and can play all games equally, which is why the PC game industry is so different from the console realm.
You know what one console would mean? It would mean that ten years from now we'd still be playing with our PS3s at Sony's mercy until the market tanked due to the prolonged flood of "nothing new". But there will never be "one console", not with a video game market in the billions. If Nintendo, Sony and Microsoft merged tomorrow and released the PiiS360 on Friday, Apple or someone else would announce they're developing a new console on Monday.