What is a web developer anyways? You need to know all kinds of things, and if you know them all then you can't be good at all of them.
I think the job of building websites is really like home improvement. You need a general contractor to get the specs and hire the carpenter, plumber, electrician, dry wall guy, and painter.
But, with the web it's much worse. There are literally dozens of jobs.
And you can an a security expert into this mix.