07 model

, yes that is a fairly stiff board but still not dead stiff like common wakeboards.
As has been said it's the tension that you create in your lines when you load against your kite that creates the "pop" you get off the water. There are different styles and ways of doing this, flex and non flex boards have different techniques to achieving the same goal. Some people say a "flex" board will allow them to "pop" higher, however it has been proven that neither will pop higher than the other and some people just go higher on a flex board because it is more suited to their style and not because it has flex.
Flex boards are more suited to the "back foot" loading type rider, whereas a stiff board is more suited to a more aggressive full body (hard front and back foot) type loader. With the flex board you can sort of "spring" off your back foot (tail) as you leave the water this can gain you a lot of extra height and if you are a weaker loader will help get you up there. The added bonus a flex board gives is the smooth landings, your knees will thank you.
The reason a lot of wakeboarders still ride dead stiff boards is because for one they didn't (until this season really) make boards that have flex with built in bottom shapes and fins, however now they make what they have dubbed "hybrid" boards (a combination of a wood core flex board with built in fins and contours) I'm sure we will see alot more riders swapping over in the near future. The other reason is because they are stubborn haha.
p.s. I really can't iterate enough that the production "flex" boards kiteboarding companies make for the most part are cheap rubbish. They flex because of the lack of materials and the poor placement of materials they use, what worse is they use this as a selling point... Don't be fooled.