Of course, buying new books anywhere supports authors. If you buy a new book from Amazon, the author still gets royalties (or, at least, the same percentage goes toward paying back the advance, moving the author closer to getting royalties). But there is a great value in traditional bricks-and-mortar bookstores, and publishing (and readers) will be the poorer if they go out of business.
The belief that the Internet would democratize publishing has proved completely wrong. No one reads self-published books online. Instead, we go online to buy books. But the online shopping experience is very different from going to a bookstore. When we go to an online retailer, we already know what we want in most cases. In a bookstore, by contrast, we browse, we read staff recommendations, we discover new books and new authors.
Online bookselling rewards books that already have a lot of attention. If a book gets good publicity, people know about it, and go online to look for it. But buyers are less likely to discover books and authors they didn't know about in advance. Instead of democratizing publishing, the Internet tends to reward success (or publicity).
Now, I'm not knocking publicity. We all hope for it. We love it when we get it. The books that receive a lot of press usually deserve it. But the world is richer for those little-known writers who rise up out of nowhere, who ride the word-of-mouth tidal wave that booksellers often start.
Booksellers are in trouble. Our culture will be poorer if they go out of business in large numbers. Please, make a point of dropping by a bookstore, maybe getting a coffee if they sell it, and browsing. You just might find something you never thought you'd buy—and you'll be doing future writers, and readers, a favor.