Dino, That advice might make sense if you happen to live next door to an "authorized" Nikon service center. I live in Colorado Springs, the second largest city in Colorado. The nearest "authorized" Nikon service center is in Denver. So a sensor cleaning by an "authorized" service center would require not only the 40 or so bucks for the cleaning, but a roughly 150 mile round trip and the loss of the best part of a day.
But even if you live close to a service center, I question the validity of the advice. Of course any Nikon dealer would like to make a few more 40 buck pops from sensor cleanings, especially since he understands how simple the procedure is. Cleaning a sensor is a long way from rocket science, and any DSLR owner should know how to do it. In addition to Mark's quite comprehensive coverage of the subject here, there's a ton of information on sensor cleaning on the web. All you need to learn the essential information on the process is a computer, a browser, and Google. Once you've done it twice you'll stop sweating it.