Staining is a matter of personal taste. If you want an aged look, most folks end up staining. Staining helps to bring out the character in the wood while, in most cases, sealing up the wood as well.
One reason you don't see hardwood floors stained in pamphlets and such is for marketing purposes. A stained floor from a perceptual perspective doesn't look new. So if there is any staining, it's a natural stain or a very light one. Also, an unstained floor in these pamphlets will show imperfections in sunlight which, I guarantee you, you won't see in the pamphlets! Another reason most folks don't end up staining is because they're talked out of it. It increases the price of the job while at the same time you're usually told that a 'dark' floor will show UV damage over time. This is because of the effects of UV light over time. It's not an easy decision but these are things worth considering.
I suggest that if you're putting a floor in a sunlit room, you use a slightly tinted stain. And conversely, if you're putting hardood in a dark room, you use a light stain. In sunlit rooms, you're best defense agains the sun is blinds, curtains, and a good UV finish. Pre-finished Engineered and solid hardwood floors have 5, 6, even 7 coats of finish. Since they're applied in the factory under ideal conditions, you're gonna get a durable, long-lasting finish. Unfortunately, this technology has put the professional installer at a slight disadvantage because he can't duplicate ideal conditions to apply a finish at your home. At least putting on 5, 6, or 7 coats requires a lot of time, $$$, and experience to do the job. With a pre-finished floor, there's only prep work and installation, and is usually done in a day or 2. An installed, unfinished floor will, as I said, take longer and cost more and you're not likely to get the same 'quality' that a factory-applied finish can provide. This is not to say that a professional is incapable of doing their job any more. In fact, they've been doing this work for hundreds of years before factory finishes came along! It's a very skilled trade and not just anyone can do it. It's just that in this day and age, technology is more and more creating and assisting in making better products at the expense of the paid professional's limitations.