1 - This is how I see the game.
2 - These people skipped the story.
3 - Correct
If you enjoy story, then take your time and level. Don't rush it. Now the reason for some people rushing to hit cap is so they can start on end-game stuff, which is enjoyable for many people who don't care about the story.
And they will be adding new content via patches, and if I recall an interview correctly, the story doesn't end at 50.