Both intel and AMD certainly could build motherboards. IIRC, intel does. The makers you are asking about build boards with different market segments in mind. They will include or exclude different features such as allowing up to 8 hard drives or 2, 4, 6 or 8 RAM slots, 5.1, 6.1 7.1 audio or 10/100 or 1Gb networking. It depends on what market segment they are looking to sell to, such as entry or value i.e. cheap, full size or micro, big vs. small size, high cost fully featured boards for high performance such as for gamers or high performance computing. the prices will reflect the end use. For a given CPU there could be a range of 20 to 40 boards with prices spread as much as $300. It usually depends on the intended use. I wouldn't buy a $300 board to use with a very inexpensive CPU and minimal RAM as I could buy something quite acceptable for under $100. The basic difference between a chipset and a motherboard is that the motherboard uses the chipset like a skeleton on which to hang the other parts to flesh out the whole thing. The chipset could also be likened to a nervous system that allows the different parts to send messages to each other.Good luck.