So here is the part of the LS which is the basis for the DCP.
"Now in the presence of the Buddha
let him come forward and speak his vow!
This sutra is hard to uphold;
if one can uphold it even for a short while
I will surely rejoice
and so will the other Buddhas.
A person who can do this
wins the admiration of the Buddhas.
This is what is meant by valor,
this is what is meant by diligence.
This is what is called observing the precepts
and practicing dhuta.
This way one will quickly attain
the unsurpassed Buddha way."
What I want to know is what Chi-I has to say about it, because I don't see where they are getting that the vow cannot be broken. We have the quote, but I think it comes from the Hokke Mongu and chapter 11 hasn't been translated yet. Probably won't be in my lifetime unless ION gets a bunch of money and we feel we can commission the translation.

funny when i was with Nshu I don't remember them talking very much about the Diamond Chalice Precepts; maybe they had some sectarian bias?
They probably don't want to appear to be on the wrong side of OE thought and it is very similar, but SGI shouldn't be saying the we are all Buddha's thing anyway. It's just ridiculous, and I know that Shoshu doesn't say it.
The Hongaku Shiso debate has been raging for over 1000 years and is not limited to Nichiren Buddhism. I believe Zen got the distinction of being the first sect that crossed the line, so to speak, and then Pure Land, so Nichiren was definitely aware of it.
"There is nothing whatever which differentiates samsara from nirvana; and there is nothing whatever which differentiates nirvana from samsara. The extreme limit of nirvana is also the extreme limit of samsara; there is not the slightest bit of difference between these two"
This quote actually addresses purity of the mind which leads to the purity of the environment and has its basis in the Vimalakirti Sutra. Nichiren does much better here saying; "If the minds of living beings are impure, their land is also impure, but if their minds are pure, so is their land. There are not two lands, pure or impure in themselves. The difference lies solely in the good or evil of our minds."
A lot of Buddhists don't understand this concept at all, and it is one of the ways that one can distinguish how far along the path someone is. Just look at their environment, which is a reflection of their mind, and you can tell if someone is full of hogwash or not.

Now, that may be hard to do because people see only what they want to see based on their own conditioning and not the reality as-it-is, so I wouldn't recommend judging people until one is at a point where they can be judged as well.
The observer and that which is observed are everywhere produced by the matrix of causality and conditions. In all that is produced by causality and conditions, there is emptiness of self.
The Great Calm-Observation, Volume 5, Part 3, Page 1