The Sabbath day has a particular significance as the perpetual commemoration of God's creation of the universe, as explained in Exodus 20:10 which you just posted - the LORD blessed the seventh day and hallowed it. See also Leviticus 23:3 "Six days shall work be done: but the seventh day is the sabbath of rest, an holy convocation; ye shall do no work therein: it is the sabbath of the Lord in all your dwellings." It is a specific day of rest ordained for all time, not merely a requirement to rest on any one day in seven. And yes, you are correct to say that this rule is also binding concerning a man's treatment of his employees. It is true that it is not nessecary to slavishly obey the letter of the Law, but nor can one change the meaning of the Law to suit their own purposes.