Exodus 21: Punishable by Death?

In Exodus 21, Moses gives a number of judgments to be set on his people. my questions is:
Do these judgments still apply today?

i understand that some of the judgments such as the terms of selling slaves does not apply today since we dont have slavery. but we do have disobedient children that strike their parents. Exo. 21:15: "And he who strikes his father or his mother shall surely be put to death."
is there any reason why we dont follow this?

I have a couple of theories:
1. its just a test that God specifically placed on these people. because they've come out of Egypt and God wants to get rid of the influences and practices that they've picked up while in Egypt. After Moses presents the 10 commandments, Exo. 20:20 says:

"And Moses said to the people, 'Do not fear; for God has come to test you, and that His fear may be before you, so that you may not sin.'"

So I think that God put these harsh punishments on these people so that they would be afraid to sin. It was probably the only way to teach these people. I mean it DID take them like... 40 YEARS!
but did they ever lift these judgments? did the jews still go by these laws? if they did then that brings me to my next theory...

2. By the grace of Jesus, we dont have to punish each other by death anymore.

but... why does America still have the death penalty? Exo. 21:12: "He who strikes a man so that he dies shall surely be put to death"