A: You do have more than AMD and Nvidia.. but all the others are focusing on specialty market. Like Matrox focuses on deliver graphic card for video walls (walls of screens). And of course, you have Intel, which OEM loves, because the GPU is a free one, making them pick that over Nvidia and AMD offering, as most of the consumer don't know any better, or care. Does it surf the web somewhat? Does it run Office? Is Windows experience somewhat smooth? And is the laptop or desktop the least expensive as possible, even though opening the box once purchased and seeing the produce in one peace, is a manufacture error (yea, I went there), then Good! They like it, and that is what they buy. Nvidia and AMD doesn't have a chance. That is why Nvidia started Tegra recently, and playing catchup with the big guys (surprisingly they are doing leap and bound at every generation.. I expect Tegra 5 to actually be kick-¤¤¤.. maybe not the most powerful of all of them, but most likely superb value for your money). What helps Nvidia with Tegra, is the company extensive knowledge on graphic card, and able to deliver graphic performance on a what it would otherwise be a weak chip, with excellent efficiency and low power. Also, Nvidia focuses more on Quadro and Tesla series graphic card, as this is where the money is.. not consumer products (not that it's nothing, it's pretty big, but not the main inputs of money). As for AMD, they are focusing on their APUs. If AMD can make their CPU in the APU more closely match Intel CPUs, then it would take the win and a massive increase in market share.
You used to have a longer list of consumer gaming graphic card, if you will, back in the old days, but they all closed down, or got bought by other companies, or made them change market like Matrox. Bessie best performance, and value for your money, another issue was business models not working for companies, as a new business model had to be put that didn't exists from text books, or used by other businesses.