I think the reason for this is that ranged units should be squishy if melee get through to them, but you should not be able to one-shot them with ranged. Imagine having a ranged unit stationed in a city, picking off the attacker's siege units one by one. This would not be fun. Also, if I am not mistaken, this works the same in vanilla Civ5, this is not a VP thing.
I personally reduce both melee and ranged strengths for all archer-line ranged units a bit, because I find them too durable when attacked by melee and too powerful when you amass them in one point on the frontier, but that's another topic and people seem to like the stats as they are (it always discussed in the balance thread long time ago).