That's just BS. A model S has a better interior than a 5 series or the new E class. 7 series or S class, you probably have an argument. But not compared to the midrange sedans.
I agree with Mike. In fact I don't think it's close - the German cars are much, much better. And it's getting worse. Fewer options, no leather... Now, I still think a Model S with the 21" wheels looks better than almost any car on the road (especially the face lift cars). And the overall experience is still more exciting to me than anything BMW/ Merc has to offer. But the interior and panel fit are still way sub par.
I had planned on getting a Model S later this year. But if they don't refresh the car pretty significantly, and offer more compelling interior options, I think I will wait for a maxed out Model 3. I think that spartan but high quality 3 interior might really grow on a person. For a fraction of the cost.