I think I have found a reason for the Euro gauges to be dim. If you look at the back of your stock face gauges, you will see that some area are intentionally made more dense. It is perfectly logical, for the light from the bulb cannot have the same intensity everywhere. So in American gauges they they made dim areas right where the light intensity would be the greatest as to supress it a bit thus making the entire face gauges evenly lit. In Euro gauges, however, different areas made dim--to be more precise, where in American gauges the area is most dim, in European gauges it would be least dense, and otherwise.
From this, I came to a conclusion that in European instrument clusters the bulbs are installed in different spots.