There is a difference between D’Oraisa and D’rabbonon. The chiyuv is not the same, the onesh for being oveir on each is not the same, and the permissibility to suspend the latter is less strict than the former (in an emergency that is not pikuach nefesh).
Likewise, the chumros of our rabbonim, though we must observe what they tell us to do, are still not the halacha m’Sinai, but rather are gedarim that we follow to preserve the halacha m’Sinai. So there is a little wiggle room (as per our rabbonim) within some of those areas, as well (such cholov Yisroel).