Subtle impatience with "would"?

Question

In her work, Sabine forgot to check the validity of some figures.
Robert, one of her colleagues reviewing her work before approving it, wrote in his remarks: "Wouldn't we need to check the validity of the column 3, as well ?"

My question is:
1- Why didn't Robert simply say : "Don't we need to check the validity of the column 3, as well ?"
2- Is there any subtilty between the two questions ?
I have the feeling that the one used showed that Robert was a little impatient with her work.
Especially when using a question.
Because, if I were reviewing, I would just say :
"We also need to check column 3."
"Please, check column 3."
or
"It looks like you forgot to check column 3".

Thank you

Answer 1

1- Why didn't Robert simply say : "Don't we need to check the validity of the column 3, as well ?"

Robert is being polite.

A reference from The Chicago Manual of Style Online:

"And according to the American Heritage Dictionary, “would” is used to make a polite request. But then again, a similar thing is said about “could”: “Used to indicate tentativeness or politeness. I could be wrong. Could you come over here?”"

2- Is there any subtlety between the two questions ?

"Don't" is more direct, and lacks politeness. There are many situations where directness is fine - it's not always required to be overly polite.

I have the feeling that the one used showed that Robert was a little impatient with her work.

Not necessarily.

Any time that one person mentions another person's mistake, we might wonder "Is he impatient/annoyed/angry/disappointed".

You could also argue that using a direct tone indicates impatience because you don't even have time for basic politeness. Thus, it could go either way.