Well first of all you need to keep in mind that companies like to stretch the info to make their products look better so they come up with unprecise terms to describe how they function.
Bottom line is that you can't add information to an image, thus when you upscale you are not increasing the quality of the picture. BUT not all scalers are equal and some do a better job than others. There are also filters that allow you to remove the noise in the picture as well as sharpen edges etc... (that can be done throught a HTPC, or a fancy upscaler). In such a situation the picture quality could therefore improve if the scaler in your TV/PJ sucks.
But that image would not be close to the quality that you would get if the image was already at the native resolution of your TV.
