Piping line stock does not use material density

[ErikClacey]

In Creo 4, M080, one can create a pipe line stock and choose a material source file. Yet the option of entering a weight/length option still exists. This gives an erroneous pipe density and mass. The material file includes the material density, so why does the piping line stock not use the  correct values and relies on a weight/length value, that has to be recalculated if the pipe diameters are slightly changed.

[KenFarley]

I've not used the routing module, but will hazard a guess that it's done to accommodate the variety of piping available, such as reinforced plastic, bimetallic pipe, pipe with copper shielding, etc. They're likely trying to give the options so weight estimates will be good?