Happy to be able to read my kindle books on my computer. Not that I plan to do that often, but it is a nice thing. On my iPad/iPhone, I'll continue to use the kindle app.
When you click on the "Kindle Store" button in the web app...it takes you to the regular ol' Amazon kindle store website. The same site I've used all along to buy my kindle ebooks. I still don't see the "big deal" about having that button removed from the kindle app. It's no trouble to fire up safari and type in amazon.com