His slave was assisted by an anti-slavery group that was pretty prevlent at the time, which suggests that slavery wasn't simply "the way things were".
In fact, the program went on to say that, as he was dying, Washington changed his will to specify that his slaves would be free after his wife died. This was also an indicator that he knew he was "in the wrong".
After Washington died his wife immediately freed all the slaves out of fear for her own life (because the slaves would have a vested interest in her own demise). This indicates that the slaves were not at all happy with the arrangement.
The interaction and history that Washington had with his slaves, as well as the fact that an underground railroad was already established, just suggests that, as a nation, we already knew that slavery was profoundly wrong.
Washington himself was not a wealthy man, his brother being the oldest inherited everything from their father. George inherited Mt. Vernon from his brother upon his death. George then set out to find a wife. Martha was the Richest available woman, she owned all those slaves. All her fortune became his, so this could indicate that George on his death bed knew he owed more to Martha than simple abandonment.
If she was in fear for her life, she would have been in fear through all the years George was not home, but out in some campaign of the war, and that was many a long periods of time.
Whatever happened, as Americans we do owe General Washington a great deal of respect.