Well, the benefit of going through your local bookstore is ... you're going through your local bookstore. I would rather give money (at least some of it) to a local small business than to a huge national/international corporation; it's a personal preference. I know other people who share that preference, so for us this is a way for at least part of our money to go local rather than national. If you don't care about it, you can buy elsewhere.

And, yeah, Google's bookstore needs lots of work. (Seriously. They're Google. They should be able to afford product testing and a usable interface.)