The Beatles did cover some early rock because they were showing their respect to the musicians that influenced them. They did write all their songs from their 3rd album on. By the way, they did use distortion, a lot. Listen to Sgt Pepper again, an album that most rock musicians list as one of the all time greatest.
Whitesnake, you are very correct to point out that the US music scene is not the biggest. There are a lot of artists that are huge in the rest of the world that we never hear of here. In fact, Americans seem to catch on late when it comes to this part of the music world. The only reason they ever want to hit it big in the states is because of the ammount of money to be made here. Not that they don't make a lot elsewhere.
Remember, Jimi Hendrix was a hit in europe long before he was in the states.