I think it's a purely political decision. If the census doesn't count Latinos, then no government sponsored, accurate count of Latinos exists. This whole race vs. ethnicity thing is kinda unthought out, really. Race is really a political thing in this country.
By one set of arguments on the board, Latino is just an ethnicity like German American is. That really doesn't make sense to me. Latinos don't come from one country or one region. The comparison to German American would be Cuban American or Mexican American or Peruvian American, not Latino.
Others point out that old forms list White Latino and Black Latino, respectfully, I think that comes from the Jim Crow days when some Latinos went to White schools and some went to Black schools based on how light or dark the Latino was and what the prevailing attitudes in the region were towards Latinos.
Whites are, by definition, people who consider themselves mostly descended from people who originally came from the general region of Europe. Black are people who consider themselves mostly descended from people who originally came from Africa - except that some people who consider themselves black do not, per say, have a majority of African in them, but are from the Black community, so it's right and proper for them to consider themselves Black if they wish. Asians, of course, have every reason to be ticked, as that category encompasses some wide-ranging, completely different folks, but it's the category folks from the USA lump them into. Go figure.
Latinos hail from somewhere in a new world country that was colonized by the Spanish, hence Latinos. (I always waver on that definition. . .Hispanic defines that better. Shouldn't Latino be enclusive of Brazil, as the Portuguese speak a Latin language? Would someone Brazillian help me out here?) That's no different from hailing from a country colonized by pale, pasty people who burst into flame when exposed to direct sunlight.
Also, if I were a conspiracy theorist, which I'm not, I might wonder if excluding Latinos from the census serves a two-fold purpose of attempting to wipe out the Aboriginal populations earlier by pretending they're dying off. Most Latinos I know have at least a drop or two of Indios in them, even my California Spanish friends with the geneaologies that date back to Spanish occupation usually have one branch or two that kind of trails off and hasn't been kept up.
Also, to the point of the conspiracy theory, even if your quantum is 100% American Indian, you can't claim it unless you're enrolled in a tribe. But for every other tick box on the list, you can claim whatever you'd like, whenever you'd like. So Lady Gaga can claim to be Pacific Islander and Black, and Seal can claim to be White and Asian and that is totally accepted. But someone Indian on the outs with their tribe just has to mark "other" and move on.
Which brings up the point that race is pretty arbitrary in the USA. A lot of people with a little Black in them don't claim it, and a lot of people with a little White in them don't claim it and no one makes a fuss. When someone does claim all of his or her ethnicities, they usually get slammed for it pretty hard, and then there's the fact of how innaccurate racial typing is in this country.
Anyway, off my soap box. I have to get ready for work.