As people have already said, that is instance based and thus is pretty biased. If you think about it, the average Arena game lasts what, 5~ minutes? It also has between 4 and 6 people in (lets say the average amount is 5, although there is probably more 2s than 3s played daily). Lets say a raid lasts 4 hours, although multiple nights might be spent in the same raid instance.
So, in 4 hours, 10 people raiding has created: 1 PvE Instance
In the same 4 hours, 10 people PvPing has created: 96 PvP Instances*