I dunno Jane, I think it's possible that Suarez' attempts to educate us all would be more effective if he wasn't wrong. I am not in the same boat as most of the foreigners who post here, I've been speaking spanish on a more or less fluent level in many different countries for over 15 years now, and have attended several years of University in Spanish only Universities.
The only points I am trying to make are that:
1) Calling a whore a slut is not incorrect in any language, it's generally a good guess since whores are usually sluts who've gone professional.
2) Puta can be used to refer to prostitutes. I have a beautiful wife who speaks only Spanish and who assures me that a puta is a prostitute. It seems the term we use in English (bitch) to refer to a generally disagreeable PMSing woman who won't shut the hell up doesn't exist in this culture (I mean a word for it, not the syndrome, which I can assure you is alive and well) "perra" (bitch, literally, female dog like in english) is also generally assumed to mean prostitute. In fact almost any insult you can apply to a woman in spanish means "prostitute" in some way. (OK, I made that last part up)
3) "Cuero" is slang (when used to refer to something that is not leather or "hide".) There is a good chance I am wrong about this, but I am waiting for somebody to prove it to me. Generally though, as detailed in point #1, I don't object as much to Suarez' insistence that prostitutes are "cueros" as I object to his claim that they are not "putas" even if he's right and puta means slut and cuero means "whore", (which I doubt) this doesn't make it wrong to call a whore a slut.
4) People should learn to speak properly in any language before they start learning slang. There is no shame in using slang by choice, but when it's all you know it shows you up for an ignorant fool. If you are just learning spanish, you should stay as far away from the local dialect as possible, refuse to use it and insist that people you deal with use proper terms for things, and pronounce at least 50% of the consonats in any given sentence. (yes this includes "S" and "R"). If you do learn local slang, don't let anyone know about it. This is lots of fun, you can often catch locals conspiring against you in front of your face because they never imagine you have penetrated their "secret code" slang.