That's interesting. I actually found having the jump and shoot actions over on the left hand quite intuitive. I'm now wondering whether left/right handedness or some other physical factors are involved in this...
Just make UP work in addition to X. This way users with built in reflexes won't feel punished.
Also, make space work for jumping too. I hit space a few times causing me to skip down on the page.
You don't need to advertise these additional key bindings, but since they are very common in other games a significant portion of players will automatically use them.
