It's okay to be concerned fuel mileage, any smart person world make sure they understood the operating costs before buying a car. That doesn't mean he can't afford it. Alot of people can afford to drive gas guzzling V8s,v10 etc. They just don't want to or choose not to.
Initially I had the same concerns before I bought mine, but I knew going into it that was going to be the trade off for the performance you get. That said, I now know that it isn't as bad as people make it out to be. (Atleast not for my driving). Now if the S65 couldn't do better than 10MPG on the highway or only made 200hp that might have effected my buying decision. Reports indicated that 15-20 MPG was more the norm, and I was okay with that. Not that I couldn't afford to drive it at 10MPG if I wanted to, but because i'd be driving it as a daily and i'd want to be able to do long trips. <10MPG would be okay for a weekend car you take on short drives, but unless you have a really good reason to it usually doesn't make sense to most people to drive something that inefficient.
It's also used as a comparison tool, I wouldn't buy a 2dr coupe that only made 200HP and got 10MPG if I was already driving a 2dr coupe with 240HP and got 28MPG. Unless of course there were other factors.
So I wouldn't say everyone has to drive a Prius if they are concerned about fuel mileage.