> my default view is that I don't want to lie or over-promise
This is the greatest prejudice around marketing in the tech community. A simple exercise you can do that debunks that frame of thought: lies are unsustainable.
Unless you're a government or a monopoly that has their predictable flow of revenue, lies aren't affordable.
You can lie and scam people, but that's not a long term strategy, because you'll burn off customers, and complains, reports, refunds will start to creep in and - unless you're in China or some country that turns their sight away from these practices - you'll be burned.
What you might think of lies is the way one can phrase a, for example, value proposition of a product: just because a big slice of applications are CRUD apps, that doesn't define them. It doesn't help anyone when it comes to perception, because that's what you have to work with - and perception is as good as reality.
You can't work without the facts, because that's what people will have at the end.
Picking on your example, there's more to a car than MPG - and even those variables sometimes are compromises. Imagine the Toyota SUV has an higher MPG because the car weights more due to some security features, and they place the SUV in the market as a SAFE SUV FOR FAMILIES.
That's a fact (in our exercise). It's also a fact that it has high MPG, but you're not hiding it either, you have to display that information and you can even justify it, but you're not spending money to tell that.
Why? Because you can only say much to grab people's attention and to deliver the right message to them. Attention is precious, you have micro seconds to snatch it and seconds to sustain it and deliver a message.
Plus you can only factor in so many variables into a decision making process, you'll always make compromises as a customer. For a lot of people MPG isn't a problem. For some, it is. That's why there's so much variety in the market.