JohnnyO,
That is not true with modern Halogen bulbs. Older conventional bulbs would allow microscopic metal particles from the filament to be deposited on the inside of the bulb's glass which will cause the light to dim over time. Halogen bulbs do not do that, so they will be as bright years later as they were when they were new.
Now that does not mean that the reflector cannot become dirty or dull from moisture or condensation which will reduce the amount of light beamed down the road, but that is not caused by the bulb.
The brighter light from bulbs like Silver Stars are created by the bulb design which includes a higher wattage, special curved internal bulb reflectors, as well as a higher output because of the higher Kelvin temperature and whiter color of the light.
...Rich