ok, I can look up rules too
In the players handbook it clearly states that when prone you grant CA in melee, you get +2 to ranged defenses, you take -2 to all attacks...AND YOU ARE LYING ON THE GROUND.
It isn't just some common sense, or webster's definition, it's actually in the rule, and by it being there, doesn't that imply that before you are prone you are....you know...NOT lying on the ground???????
You are getting too technical and focusing on the one piece of the condition with no mechanical effect. However, any creature has a method of moving itself that involves contact with the ground. A snake and a man both use contact with the ground to move themselves about, a snake has more contact with the ground, relative to its total surface area than a legged creature. A snake moves along the ground by manipulating its ventral scales along the ground. The ventral scales are located on the underside of the snake. Essentially, when a snake is moving, it is not lying on the ground anymore than I am moving if I am lying on the ground. The part of its body responsible for its locomotion is in contact with the ground and active. If you disrupt that, the snake has to right itself to move again, in that space, when its ventral scales are not on the ground, or not enough of them are, THEN it is lying on the ground. Otherwise, it is moving along the ground just as any other creature does. Lying on the ground implies a lack of movement, and indeed, the lack of movement is part of the mechanical effect of the prone condition.
Secondly, having the prone condition applied in no way implies that you weren't previously on the ground. You could well have been. There is no requirement that you are standing in order to have the prone condition applied or re-applied. In most cases having it applied again would have no in game effect, it would just be ignored since you were already prone. However, some powers might apply a duration or another situation to deal with such as entangled or a more severe penalty.
So, to sum up:
1. A moving snake is not lying on the ground, it is moving along the ground. An attacking snake is not lying on the ground, it is coiled to strike, raised up in a position to both strike and move.
2. Often conditions are secondary effects. The rules specify that the longest duration applies when a condition is applied twice by different attacks. Someone proned by a secondary effect is then hit with a command type spell with (save ends), the caster commanding the target to be prone. They are prone until they save. Same with blind, deaf, whatever.