Thanks for the suggestion. The built-in Windows 8 toast notifications I believe only work outside of the app that triggers them. And as you mentioned they are a bit large and bulky and we're going for minimalism here in how they popups interact with the UI. So in a sense, we want them to look a bit different here since they server a different purpose than the Windows 8 toasts, and are fired off more frequently too.
Another thing is that with our own, we can position them below things like the find/replace pane, and other panes coming in the next version.
If you have specific use case scenarios where you'd like to be able to dismiss them faster somehow, please feel free to offer up any ideas.