The example of differentiated instruction grading given in the talk I saw was stuff like "draw the floorplan for a house" with points for decorating, which equaled the same number of points you could get by calculating the area of the rooms.
In another example, you gave a sheet of 15 problems, assigning a variety of points to each, and told them "do enough problems to get 20 points." There were, say, 10 1 point problems, 4 2 points, 3 5 points, 2 10s, 1 20.
The top example is exactly the kind of thing I worry about with tiered homework in differentiated instruction classrooms.
What do you think of the second?
Again, what worries me is hidden tracking inside a classroom, where the bottom kids simply carry on doing the easiest problems year after year without ever advancing to more difficult work.