Unless you don't have to be using Mavericks, and it works with the latest version of Safari (assuming you have it launched) regardless of OS (Windows, OSX v*, etc), and Mavericks is only required when you don't have Safari running.
Safari also supports the "Web Notifications" specification[1], which allows a website to post a notification while it is open in Safari. This has been supported for a few releases now and is also available in some other browsers. I believe Gmail can make use of this to call attention to new emails while open in a background tab.
[1]: <https://dvcs.w3.org/hg/notifications/raw-file/tip/Overview.h...
Because as far as the user can see, Safari is the interface to these notifications: that's where you get the prompt to subscribe to the notification, and you can configure or remove notifications from its settings.