For most teachers and students, if they have a 100 point assignment and a 10 point assignment, they expect the 100 point assignment to be worth 10 times as much. But when using the default "Mean of Grades" for computing summary statistics in 1.9 Beta 2, it normalizes each assignment to a scale between 0 and 1 before computing the average.
I very much doubt that any teacher computing grades with a manual gradebook would do this type of computation. Moodle 1.6 did not either. Hence it will be very confusing and not the desired behavior for most users.
For example if a 100 point assignment received 90 points, and a 10 point assignment received 8 points, the an expect grade would be 98/110 or 89.1%. The 1.9 Beta 2 gradebook returns 85%.
If normalizing grades before computation is to be retained, IMO, it should be an advanced option and the default in computing the mean should use point values. If there is currently a setting for this, it should be the default and it's location is not obvious.