The purpose of the previous post was to solicit comments.
Now back to the real stuff:
The gemara says that only descendants of dovid who are kings can sit in the azara. Mishneh L'melech (Beis Habichira 7:6) writes that Rashi in Sanhedrin 101 says that it is d'oraysa from halacha l'moshe misinai. Rashi in yoma 25 and 69 quotes a pasuk of "la'amod l'shareis". However, the Mishneh L'melech has the most difficulty with Rashi here in sotah that says it is not kavod shamayim to sit and even the mal'achim didn't sit, which implies that it is only d'rabonon. But, he then proves from rashi himself that he holds it is d'oraysa but he is giving the rationale. Because when Rashi says that descendants of dovid can sit because "Hashem gave them kavod" implies that both the issur and the exemption for beis dovid are d'oraysa. But Tosafos in Zevachim 16 d.h, hagaha, seems to be unsure about it.
Out of all places where rashi can give the rationale, is there any reason that he chooses the context of this gemara to explain that the purpose it to show kavod? Perhaps it is in line with the previous gemara of showing kavod for the talmid b'makom ha'rav, here too Hashem showed kavod for the descendants of dovid even in his presence. v'dok!