Chris,
While you are learning to jump, it is probably not a bad idea to use a steady throttle all the way off the jump. However, to say that it's the only way to jump a thumper is simply not true. I jump different obstacles with the throttle chopped to wide open depending on the situation. You just learn to adjust with your body position. If you jump with the throttle wide open, you make up for it with having your body more over the handlebars. If you jump with the throttle chopped, you have to get back like you are going through the whoops.
If this seems overwhelming right now, don't worry. Take your time and learn slowly. If you think about what you're doing on the bike now, it will all be second nature in a few years.
Good Luck,
Stace