Jorgen Thelin [1] points me to this article questioning "What Makes a Good Integration Developer?" ?

Over time, a number of statistics have shown that the top developers outperform the average developers (not even talking about the bad ones) by an order of magnitude or so. As it turns out that the top developers do not earn 10 times the average salary, these guys (and girls) are a steal. Every company should then aim to get a hold of these "top quartile" developers, assuming the individuals demonstrate a minimum amount of social behavior.

Of course - as DB noted - you could say "Average developers are expensive" - but that's way to negative, isn't it? :-)