Paul, in the US the msds came about after concerns related to employee exposure to hazardous materials in the workplace (this is called the hazard communication standard and it's detailed in 29CFR 1910.1200) as an add on they have been including disposal information but it it not a regulatory requirement because most of the time materials being disposed of are not the same as they were prior to use, they will have other "stuff" mixed in.....solvents wind up containing some of the stuff they cleaned off or disolved for example. Additionally a compound after it has set, dried or been used may not have the same hazards it originally had prior to its use (latex paint, sealing compounds, some glues, resins,etc...)
Under regulatory guidelines (primarily 40CFR in the US) waste materials must be evaluted primarily for flammability, reactivity, toxicity, and corrosivity prior to storage and disposal and using the msds is not really the appropriate way to do this...nor is it the reacognized acceptable method. The msds may provide some guidance but it will say to look at the specific leaglrequirements prior to disposal.
I don't get too wrapped around the axle with msds's either.