It depends whether the job and your doctorate are in the same area of expertise, which I don't think you mentioned.
The answer you're pointing to speaks about omitting a certain piece of information from a CV, because the person applying to a new job does not want to work in his previous area of expertise and doesn't even want to be connected to it. That seems perfectly ethical to me.
But when you're applying for a job in the area of expertise that is the same as your doctorate, then not telling this to your possible future employer is – in my opinion – a typical example of hiding important information. Pretty much the same as problem discussed here.
From this point of view, whether you're hiding information about one of your previous positions of employment or hiding one of your university degrees, it sounds in both cases as a specific form of lie. That's not ethical at all in my opinion. Saying that I did three stages of education, not four, is pretty much the same as saying that I have work experience in seven, not eight, companies. I'm "silently" forgetting about one of them in both cases, right?
Consider what you're going to say if your interviewer finds out (by any means – piece of cake in our Facebook-like world) that you're actually a Ph.D., not merely an M.A. holder. He'll straightly ask you: "Tell me, why did you lie in your resume?"
If you're looking for a job in a completely different area of expertise, then answering such a question is pretty simple. "That's not a lie. I found this information completely not relevant to current interview process, as I don't see any connection between metallurgy, in which I have my Ph.D., and IT, in which I would like to work."
But, when you're applying to a company in the same area of expertise, then answering such questions could possibly be embarrassing and that's why the whole situation sounds pretty much unethical to me.
Finally, consider that in certain countries (like my homeland Poland) not mentioning your real education level is considered illegal according to local laws and regulations, as it is a lie in fact.