The better impedance control on the line results in lowered reflections & hence probably lower jitter BUT is it not true that the attenuation also knocks down both the signal & the reflections & each round trip of the reflection is attenuated further. Is this not the same effect as a well terminated cable where less signal is reflected to start with & each round trip it is attenuated even more? A visual of reflectionshttp://en.wikipedia.org/wiki/Reflection_coefficient
Of course, it attenuates both the signal and the reflection. Who has tried to convince you of something else?
Any method that knocks down the reflection is beneficial. There are more ways than one. Some have the effect of also making a better resistive match. It isn't rocket science. Don't ask me why this isn't taught anywhere. Techniques like this are older than I am.