No objections so far, but this doesn't seem take into account that the utilities will want to load balance night charging even then (not because of transformers, but because of other parts of the grid and because of power plant availability), and at night you'll have more power available than at peak, and at specific times during the night you'll have even more power available, so ideally you'll want EVs to overlap in that area, or even some EVs to charge only in that shorter period.
So I'd expect that while they will want to put a limit on during-the-day charging, they will eventually welcome the flexibility that comes with higher charging rates. If the charger itself is limited to 6.6 kW, then there is no possibility to take advantage of the most optimal time in the night. Whereas otherwise the charger or the car can still be set to a lower charge rate if used during the day.
Once you have 500 mile batteries (this is actually IBM's goal for Lithium Air batteries), and even with 300 mile batteries as the Model S will have in July 2012, with 6 kW you cannot charge it anymore during the night alone. Think of events such as when lots of them come home after Thanksgiving, and you would't want all of them to continue charging into the next day.