I've had experience with similar perception and quality issues in the past. I'd be willing to bet money that the exact same MPEG4 effects are the same on every HD set connected to a 622 receiver, even though some people are stating that they don't see it. That is almost always due to them not being sensitized to the particular effects.
It is almost impossible that several people would see the same exact effect and yet not everyone has it. Because the effect is not TV-dependent. The type of effect described is almost certainly a MPEG4 encoder effect, and everyone is getting the same data stream through the same encoders.
Well, there could be some TV-dependency. A lower quality TV could mask some of the effects. But the better the TV, the more obvious these effects should be. A great TV will not compensate for image defects, rather they will display them in even sharper resolution & clarity.
Technically it could be due to a problem in some 622s, but that is very unlikely, as they are all using the same MPEG4 chipset.