At least, Elon is honest about it and says "this is about convincing the people that are skeptics". (And not about making a fair comparison.)
An Audi A6, in the US at least, gets 33 highway MPG and has a 19.8 gallon fuel tank.
And yes, of course you charge the Tesla more often. You charge it every night when you come home, and it's ready with a full charge the next morning. That's just a totally different usage pattern from only filling up when it gets low like you do with a gasoline powered car.
I'd bet that most Tesla drivers will never have to stop to recharge, mostly because they will use their Tesla around town, and will take long trips in another car or fly, because Tesla owners are wealthy.
EDIT: converted imperial gallons to US
That's probably true, but much of the recent marketing around battery swaps and transcontinental charging networks is aimed specifically at road trips. I suppose one would argue that they're working on this infrastructure now for the future when much more affordable EVs are available.
The only "regular" capacity unit that I know of comes from a deliberate attempt to normalize every units. Namely, the Litre from the metric system.
Smug Frenchman
With that said, it's not sensible to compare a modern european small car with the average US car. Particularly the class of car that the Model S is competing with (which are typically expensive, have a high capacity and relatively inefficient engine, and luxury interior).