Greetings SeriousFun and thank you for your question 
I think it is very good that there are such distinctions, it is much better than the alternative of them being absent.
If highly esteemed sages were giving too much loose space, people would keep having excuses “Buddha said it is OK to be so and so” and it would just perpetuate their wrong habits and conduct. But with such strong distinctions, if they believe in the text, they can check and try to analyse in their light if they’re on the path, or straying from the path.
Just take a look how deeply writings like christian bible influence how people who follow it think and act later on. Same with the suttas for buddhists. One quote from bible, which is perfect example of loose guideline being abused later by the masses:
God blessed them and said to them, “Be fruitful and increase in number; fill the earth and subdue it. Rule over the fish in the sea and the birds in the sky and over every living creature that moves on the ground.”
People use it now in discussions against veganism as excuse to enslave and kill animals for food, because God said it is OK to subdue the earth. Even thou the other place in bible say “thou shall not kill” . So it is very importaint for great sages like the Buddha and even respected monks and nuns to be very careful to say what is right and what is wrong and be specific and definite about it. Even if it would create some impression of being too black and white, it is much better than the alternative in this context. Because a lot of people look for excuses in grey areas. It is much better if grey areas arise from careful consideration and interpretation of specific guidelines, because it at least makes people think, and not just repeat “the great sage said it is OK to do that”.
So it is very importaint that suttas give us clear guidelines and high moral standard about what is good, true and right.
Same goes for the monks and nuns. People also expect that they give us very high standards of virtue without much space for doubts when we are straying away from following the path properly. Of course there is always place for forgiveness and understanding of our faults, but it doesn’t change the ideal we aspire towards.
On the other hand, I think buddhist suttas are still very much open to interpretation and so there is a lot of space for grey areas in there, check this text by Bhante Sujato for further and more authorative explanation:
the true meaning of a spiritual text emerges from context and experience, not from etymology.
Notice your own response to the text: what is inspiring, what is boring, what is dubious. Your responses belong to you, not the text.
Beware of the mind that wants to criticize the text. Even though I myself believe in the importance of text-critical studies, this is after many years of study and reflection. It takes time to get a sense for these things. Have compassion for the text. Read it kindly, as if you were listening to a beloved friend. It was composed in an oral tradition in a far off time and place. It is a miracle that it exists at all, and we should not be put off if some of the modes of expression are alien to us.
Perhaps a bigger problem is the desire to literalize or insist on a particular reading. The Suttas have a word for this: idasaccabhinivesa —the insistence that “this alone is the truth”. Any text is open to different readings and emphases. It is easy enough to find cases where modern teachers or traditional schools teach things that differ from the Suttas. It is not so easy, but far more valuable, to understand why these changes came to be made, and to understand what aspect of Dhamma is at stake.
If you are in doubt, remember the poised attitude that the Suttas themselves speak of: “Neither accepting nor rejecting, I will inquire about the meaning…”. In Buddhism, we are not expected to believe literally every detail of the scriptures; but if we read them with a fault-finding mind, we will never really get it.
Whatever aspect of Dhamma—whether meditation, philosophy, ethics, or inspiring stories—there’s nothing like the real thing. Take the text, and live it. Try it out and see what it does in your life. Meditate on it. I’ve been doing this for 18 years now, and I’ve never been let down. Whatever faults I have, they’re all because of my failing to live up to the Dhamma, not because of the Dhamma itself.
I’m sure others will have more answers and some suttas references, but I hope this quote is a good start.
Metta 