Re: Steampunk - Source Material
As a short shot into history, and in danger of tainting my own thread - it came from the fact that the original Steampunk Literary Movement (and the origins of Steampunk as a genre - literature is unsurprisingly the origin of most genres) was coined by author K.W. Jeter in 1987 to try and describe a series of works by himself and others going back to the early 80s. And as an offshoot (sometimes tongue-in-cheek) of Cyberpunk.
The Difference Engine is the most prime example (and contains an AI, in fact some have speculated the AI is in fact Wintermute) of directly transporting Cybeprunk Near Future (dystopian and anti-establishment themes along with) into Victorian Past.
As with any label, once it's identified it's easy to go back and pick out various works in the genre no matter how old - and since Verne, Wells, and even Shelley served as direct inspiration for the 80s Steampunk novels they are ultimately considered part of the genre at this point. Even some of Twain's work.
So the 'need' to be in Victorian England comes directly from the fact that early Steampunk was almost universally set in that specific time and place.