I just purchased a diesel car and diesel fuel IS at around $4.40 per gallon... I would have gladly purchased a electric car.
Tesla's price point is too high and their lower priced model is still a little ways away from release. Nissan Leaf can run only for 100 miles before it needs to be charged. This makes it a difficult substitute for a regular gasoline car because it will not be able to satisfy most Americans driving needs.
Therefore, for this prediction to hold true, its important to have enough viable options in market.