There is a popular mis-conception floating around the universe that writing is easy, in all its incarnations. There is also a sister belief that written expression is a less valuable asset than visual design or personal interaction.
I say that these are mis-conceptions because, culturally speaking, we are trained from an early age to seek written words when we need information. It can be in the form of a textbook, magazine, microfilm, web site, or even a phone book. Words, in their written form, are one of the major ways in which knowledge is transfered in our culture.
It is for this reason, among others, that paying attention to the words released in your name, even in letters, email, websites, essays and more, holds such a great importance. Even people who would not consider themselves avid readers have enough reading experience in their lives to read somewhat critically, meaning that everyone that encounters the words that represent you discover what you consider to be exemplary quality.
Ironically, the reason that the quality of written content matters is also the reason people assume writing is an easy process that can be performed well by anyone that can read. I am sure that you have encountered writing in your own travels through life that offer a resounding opposition to that idea.
Writing, like automotive repair and dentistry, is a learned skilled. However, similarly to automotive repair and dentistry, not all practitioners are equal. Some may be able to put together grammatically correct phrases, but lack the ability to give them life, where others bring life, but get lost in grammatic and spelling errors. Either scenario leaves an uninterested audience seeking another source.
It takes a certain level of commitment on the part of the writer to understand how much of each aspect needs to be inserted into each piece. This becomes a particular art form when you take into consideration that there are very few steadfast rules which need to be applied in every circumstance. It then becomes the writers ability to understand a variety of audiences coupled with a deep understanding of their skill that allows a writer to be considered even adequate.
The truth is that anyone who has learned the physical act of putting letters together to form words can write, but there is only a small percentage of people that can put words together in a way that makes you want to sacrifice a portion of your life to read them. This holds true for all forms of writing, from business letters to textbooks and all the forms in between.