Why? How? Because they're involved in software development. And before you start wondering what I'm talking about, I'd like to remind you that your web site (although cool) is nothing more than a software program running on a computer. And ever since people started writing software there have been very well defined roles and skill sets.
Now don't worry, I'm not going to bore you with roles and skills definitions for software development, however I am going to make it easy for you to figure out the type of web resources you may have at your disposal and whether they are helping your business - or unknowingly harming it (just in case you were wondering.)
An analogy that should help:
Does the interior decorator or designer of your home perform the same duties as the architect? What about the builder of your home, are they the same as your architect? Of course not, the interior designer works with the look and feel of your home, the builder erects the structure and the architect designs the master plan and oversees the development and ensures the finished product meets all the requirements (and the building code!)
There's no doubt that the builder and the interior designer are absolutely critical to the success of the project, however they follow the guidance of the architect and the plan the architect created. When put like this you immediately see it's a little foolish to assume all the roles are alike and how easily it would be for an over enthusiastic builder or designer to unknowingly cause you some problems because they had no master plan to follow.
So here's a quick cross reference and comparison for you: