My anecdotal experience has been that those salaries are accurate, on a US national average. Lamentably, location plays a significant factor in it -- salaries are notably higher in tech centers like SF and Seattle. Conversely, I've heard of dismally low salaries for rails consultancies in less urban areas (Madison, Wisconsin, in my case). Also, European consultancies tend to compensate developers less than their American brethren.
Another easily overlooked factor here is how big and lucrative the B2B custom software market is. If a consultancy can establish a reliable track record, the limiting factor on their success becomes how many developers they're willing/able to hire to handle all the client work they choose to take.
Another easily overlooked factor here is how big and lucrative the B2B custom software market is. If a consultancy can establish a reliable track record, the limiting factor on their success becomes how many developers they're willing/able to hire to handle all the client work they choose to take.