Why the Photoshopping?

I saw this piece yesterday but couldn't confirm the authenticity of the pictures and so didn't blog it. From the coverage spreading it would appear that the Sun did indeed edit a photo of Prince William and his comrades by erasing the rastafarian "driving" the boat. Three questions strike me: first, why erase the man in the first place? Second, why leave his knee there, having erased the rest of him? Third, why also erase the engine, how do they think the boat is powered?