@Marrea - Most DSLR cameras (Canon, Nikon, Pentax, Olympus and others) now have inbuilt sensor cleaners - they use ultra-sonic vibrations. I've not had a problem with my Pentax K-7
Yes, indeed, my three year old Canon EOS400D has a self-cleaning sensor unit which shakes dust from the sensor each time the camera is powered on and off. So where does the dust go once shaken off? It’s still floating around inside the camera ready to settle on the sensor again!! If these so called self-cleaning units actually worked effectively there would surely be no need for kits such as the Visible Dust Arctic Butterfly which sell at anything from £100 upwards.
You're very lucky if you've had no problems with your Pentax. I try to keep my lens changing to an absolute minimum, nearly always indoors, always keep the lens throat pointing downwards, and still I can spot dust blobs in my photos - usually seen in large areas of blue such as the sky. Nothing major yet and easily removed of course with Photoshop but irritating nonetheless.