I never understood why Nvidia never paired up with Intel like Radeon did with AMD. Ironically, I think Radeon is the glue still holding AMD together, since their GPUs still can compete (and outpace in some instances) Nvidia. I read somewhere once that Nvidia was AMD's first choice (not sure if its true), but something happened and they ended up buying Radeon instead. AMD and Radeon would trully fail I think if Intel teamed with Nvida.
You can see why though what jaduarskx pointed out about the cost to enter a new market, Intel currently is brutally embarrassed in terms of on-die graphics performance vs AMD. Say what you will about their processors, plenty of warranted criticism to go around, but Intel is years away from catching AMD's graphics. GPUs and CPUs are both microprocessors, but they're different animals in terms of design. Even a CPU company as great as Intel who has been in the business for many years is a baby in the GPU specialty.