These verses provide us with the very interesting fact. Let's take a look:
YLT Dt 5:1 And Moses calleth unto all Israel, and saith unto them, 'Hear, Israel, the statutes and the judgments which I am speaking in your ears to-day, and ye have learned them, and have observed to do them.
YLT Dt 5:2 Jehovah our God made with us a covenant in Horeb;
YLT Dt 5:3 not with our fathers hath Jehovah made this covenant, but with us; we--these--here to-day--all of us alive.
As you can see from these verses, it appears that even though Torah was known to Abraham (Gen 26:5, c.f. Ex 24:12), it appears that it was not applicable to previous generations because it was not officially given yet. This, perhaps, explains why Abraham got away with marrying his step-sister(Lev 18:9) and Jacob got away with marrying siblings (Lev 18:18).
At the same time, idea of the Torah is that it is applicable at all times, so I think God still judges us, even if we are exempt. For example, Sarah could not bear children and Jacob's wifes fought all the time.
So keep in mind that commandments of the Torah are applicable AT ALL TIMES. Therefore, be very careful and guard your soul with all your strength and wisdom by observing these great commandments!