Well, obviously they're not. But before you dismiss this as total drivel, let me explain. Like people, bookshops - even chain bookshops - have individual personalities, and though there is central pressure on appearance and the core books they stock, in the end each shop can be hugely different in how they choose their discretionary books - and in how they deal with authors.
Take a case in point: Waterstones. Our local Waterstones seems to hate authors. (Well, me.) Every time I've had a book out, I've contacted them, asking if they'd like me to sign their copy(ies) or do ANYTHING to help sell books. I've never had a reply. Once, one of their staff put a positive-ish review of one of my books on their website. I thanked him via email - I got no response, but immediately my book disappeared from the shop, never to be seen again.
Now contrast this with the Waterstones branch in the Science Museum in London. Admittedly they have a natural affinity for science writers, but they could have been equally stand-offish. They weren't. Their superb manager has been very friendly, arranged a signing event and keeps in touch. She makes it seem like they're a bookshop that likes authors. And surely that can't be a bad thing?