"You donít see very many markets where there is a Coke and no Pepsi." says 38 Studios' Brett Close, using the ever-popular soft-drink analogy. "Thatís what you have with WoW. Other products have been successful, but theyíre not the massive competitor that I know will exist."
I'd think there's at least one other case that should immediately come to the mind of anyone involved in a computer related industry...Microsoft. There is simply no competitor anywhere near their market share.