What IS that crumbly cheese on Mexican chili-cheese corn on the cob (elote)?

It is not parmesian though it seems that Mexican corn on the cob is the darling of dieters ... rub corn with non fat mayo, sprinkle with low fat parmesian cheese and chili ... aye carumba ... no, no, no.

I was checking out local Mexican markets for cheese in general, but they seem to have a few types of powdery Mexican cheese. The most common I've finding in on-line recipes is queso cotija. Is that correct? That was what this recipe says, but they also say you can use feta, so what does epicurious know about food anyway?

http://www.epicurious.com/cooking/men...

And is it always mayo and not margarine? From my local street vendors it seemed margarine was being used ... please let it be margarine because mayo ain't yellow.

Then again, while Googling, I found this interesting article about Mexicans and mayo ...

"Venture through one of the Gigante chain of grocery stores and you’ll find no less than 39 different sizes, types and brands occupying 6 shelves, each 321⁄2 feet long: original, lime, chipotle and other chili flavors"

http://www.tomzap.com/mayonnaise.html

The above link says it is crumbled Oaxacan cheese. Is that the same as queso cotija?

I've been noticing that the texture is different depending on the street vendor, some is very fine cheese and others have a slighly coarser texture.

Any thoughts on this?