This, in a nut shell, likely for the last 70 years or so, is what makes some folks blood boil. Many believe that individuals collecting disability (partial or full) while being able to perform such tasks, as you mentioned above, should be denied benefits. I don't always agree. What's easily over-looked in such a case it the totality of circumstances. Some folks just have a tendency to only look at the little picture.
In many cases, replacing water pumps can be a real PITA (physical challenge for some) especially on the side of the road. However, it's not a job position that you're expected to perform 8 hours per day, 7 days per week. Picking up cans, I suspect, is done in ones leisure with no quota or 24/7/365 involved.
Life is short and on this planet there's far more to be concerned with than a few million folks scamming the government for benefits, disability or otherwise. BTW, anyone know how much has been spent thus far for our involvement over in the sand box?