Strongly disagree. I have often finished a book and though, "hmm, that was great. I want to read the next one in the series". But wait! I have to pop over to the browser, log in[1], search and the book I want, buy it, then go back to kindle app, sync....

It could be sooo much better. Is there a next book in the series I am reading that I don't yet own? Show it on the "would you like to rate this book" page or something. Take my money amazon! Take it faster!

[1]: Which due to my own idiosyncrasies requires me to fire up 1password and copy my ridiculous password to paste it into amazon login.

... and it's not like it requires a lot of effort to switch to the web browser on an iPad. Just swipe up with four fingers and touch the Safari icon. And at that point, you don't have to deal with the terribly slow monochromatic screen.