The maps make clear a point I've harped on before: that our NYC/DC/Harvard punditocracy is completely clueless about the multi-generational prospects of Mexican-Americans.
If you look up Mexicans on the NYT's map, there were only 2,138 people of Mexican birth living in Manhattan County in 1980. A goodly fraction of those were likely scions of rich Mexicans working at, say, the U.N. and/or partying at Studio 54. In 1990, there were still only 6,003.
In Washington D.C. in 1980 there were only 514 Mexican-born residents, and in 1990 there were only 1,034.
In Suffolk County, MA, (Boston, Cambridge, etc.), there were 271 in 1980 and 1,006 in 1990.
In other words, Mexican immigrants are a new phenomenon to America's media establishment. So, it's easy to apply Ellis Island-based fantasies to immigrants from Mexico: by the third generation, they'll be doing as well as Italians! Who can say we're wrong? Mexicans in the U.S. are an utterly new phenomenon. There are no track records!
In contrast, in Los Angeles County, there were 33,644 Mexican-born individuals way back in 1920. And there were probably an even larger number of American-born Spanish-surnamed people. In 1980, there were 697,000 Mexican-born folks in LA County. More importantly for analytical purposes, by 1980 there were already a huge number of third, fourth, and fifth-generation people of Mexican descent in LA County.