I think this was discussed on another HN thread. The app is native to handle the push notifications, but loads a webview to handle the actual display of the inbox. And it seems like it loads the webview every time you view the app. Lots of Googly magic is probably happening in all of that JavaScript.

The load time led me to delete the app. But I can't get mad about the loss of push to mail.app. TANSTAAFL.