garymeyers – yes, birchas hamazon is d’oraysa. However, one would fulfill the mitzvah d’orayasa with al hamichya which is a summary of the three brachos of birchas hamazon. In fact, the second and third brachos of bentching were established in the days of Yehoshua and Dovid uShlomo respectively.
Shmendrik – the fact that it is easier to say mezonos and more effortfull, to wash and bentch does not mean that mezonos is a kula and hamotzi is a chumra. Would it be OK for someone to be “machmir” and say hamotzi on a piece of cake? surely, he must say mezonos even though it is easier.
p.s. I respectfully request that this Torah discussion not contain any more needless attacks on our fellow Jews.