I agree with internetauthor -- copywriting has been around for awhile. As long as people have been putting their words to paper, that is. What you may have observed is that their is a need for true copywriting, something that goes beyond simple web content writing. Not everyone has a gift to copywrite. Your words must be strong, informative, and persuasive and your writing must be grammatically correct.
It's definitely nothing new. Every business needs solid copy. I'd recommend reading up on sales, advertising and so forth as well. Perhaps go to college and at least minor in marketing. And of course, the more you know about a product, service or industry, the better you'll be.
Search relevance and media distribution (adsense!) have been driving factors in the marketplace, but these buyers who are interested in services for those reasons are not dealing with copywriters, they are dealing with web designers / online marketers who claim to be writers. They are not. Period. For years marketing agencies and large companies have used copywriters. Copywriting is not new, neither is ghost-writing, it is just that these services are now needed by small online businesses as well as large companies.