Probably having Apple as a customer mattered a lot to Intel, so they were willing to be flexible. The HPs and Dells of the world are important too, but they can't afford to offend Intel, since they're all in a fierce low-margin competition with a bunch of other vendors that sell basically the same product. If they're at even a slight cost disadvantage, their profits evaporate.

Apple had more leverage because they sell a product that's unique that their customers are willing to pay more for, and because they had a plan B if Intel refused to accommodate them.