From a technical point of view, I agree that scalability is a killer feature. But from the point of someone learning about key/value stores, taking a entirely different approach is helpful. For me, it has been invaluable to detach my thought process from any concept of SQL and think different.
If education and mind expansion were the point of distributed key/value stores, then this would be a valid argument. For some people, I suppose it is. But, for most folks they are a means to an end...and the end is not making people more clever. The end is building scalable applications for most folks, and an SQL query layer doesn't impede that.
