Like the two vendors said you are right in your thoughts about staggered wheels. Now the offsets concept can be very simple and easy to get a basic understanding for. However, picking the perfect offset can be a difficult task as you have to take into account your brake size, your tire size and the application of use. For example I have one of the most aggressive wheels on the boards with the following specs:
20x10 +15
20x12 +0
Now the +15 & +0 is the mm distance the back of the wheel face is from the center line of the wheel. Check out the offset discussion sticky for more explanations
