You pretty much answered your own question in your last line!
That biiiiiiiig lens is far more important than any megapixels out there. And of course the big SLR camera also matters quite a bit. It's sensor is at least 15 times bigger than that on your p&s. You see, the way camera works - lens collects the light and forms a picture on the sensor. No great camera can capture an image better than that projected by a lens. So your 12 megapixels are capturing just a so-so picture that your small and cheap lens created. Then again the bigger sensor, and fewer pixels on it, means each pixel is much bigger in area, allowing it to absorb more light and create more exact representation of the actual colors.
But the fun does not end here. It's just the optical part that we talked about. But your photographer is probably an experienced professional with years of experience. He knows exactly how to put up the lights and how to get the composition and all how to set the camera for the great shot. That is also a very very big and important part of photography. I can almost guarantee, that if you and that photographer switched the cameras for a day, and you used his big camera with biiiiiiiig lens, and he used your regular p&s camera, at the end of the day he'd still come up with better photographs than you...
That's why he's a professional, and people come to him and pay him money for his 5mp portraits, rather than taking them with their 12mp cameras at home.
LEM.
