There is a lot of Indian blood (Mayan, Inca, etc.) in Central Americans and Mexicans, as well as European Spanish. So while it's true that there are similarities, they are not quite the same.
Yeah...my cousin, who is hispanic, is blond and blue-eyed like Cameron Diaz. And, no, Sancho wasn't involved--just lots of Spanish blood there.
Trick is, of course, that once the Indian population in Mexico had gotten down to the 3 mil to 5 mil mark (from it's previous high of 50 mil), the place had to be thrown open to extensive Spanish immigration ~ and it was ~ and they are still there!