While in America it's reasonably common for there to be teabags available -- at work, at conferences, in hotels, etc. -- you'd be lucky to come across milk nearby, unless possibly there was also coffee. However, in Australia (like England), it's just naturally assumed that if you're using a teabag to make a cup of tea, you're also going to be needing milk, and it's generally hiding somewhere cool and close at hand. Huzzah!
(Sugar, too, of course.)