In fact, Language Myths discusses “uptalk” in the chapter I referred to earlier. Apparently, the spread of it to virtually all English-speaking countries in the world predates its appearance on the Aussie soaps.
Have the media any influence in reinforcing the dominant dialect in a region? For instance, are American media reinforcing American speech patterns?
Why do you Brits take a perfectly good truck and call it a lorry? Lori is a girl’s name, and trucks are big, manly vehicles. 
I’m not aware of any studies on the subject but I’d say it’s also doubtful, and for the same reason: the relationship between the media and its listeners is one of reception on the listener’s part rather than interaction between the two. And a strong impact on speech requires the latter.