Tesla is a fad. People who can afford $100,000 cars don't care about gas prices.
It's something different and new on the road but people who buy something new and different always look for something new and different few months down the road. Wait for the 20% resale value of Tesla after two years.
Sure, many people who can afford a $100,000 car don't care about gas prices, but they certainly do care about not having to take 10-15 minutes out of their day every week to stop and get gas. Time is money, and Tesla's target audience values their time greatly. Plugging in at home takes 2 seconds in the comfort of your own garage and you have a full tank every morning. This alone is worth the price of admission.
Also, people who can afford a $100,000 car care tremendously about performance and ride, and the Model S offers a driving experience unmatched by any other car thanks in part to its electric drivetrain.
For these reasons it's far from a fad and why every car magazine and motor head out there has declared it the best car ever made.