For Sale: Lo-Pro Funny Bike

The driving forces from the sprocket want to turn the hub but the road wants to keep the rim still, if you see what I mean. The cross gives the hub stability with regards to this rotation (because the spokes pull equally in opposite directions). The same support is not required on the non drive side so radial is fine. The spokes are a bit shorter so it saves a bit of weight and helps make the wheel feel stiffer because overall it has been laced in three directions (drive side- left/right, non drive - straight up). Shamal et al are laced this way and I'm sure lots of others too.

Actually if you assume the hub is stiff, I don't think it matters which side is radial and which is non-radial. Perhaps it is traditionally done non-drive side to help even out the spoke lengths and relativeness spoke stiffness.