Film, TV and graphic novels are always more focused on the look than the function of things—it goes with the medium. I once raved at an SF Worldcon about the aesthetic appeal of all that fabulous laboratory equipment in the original black & white Frankenstein movie, which didn’t go down to well with the SF-oriented audience (okay, okay, it was meant to be a panel on science). As for Victoriana, the iconic figures of the 19th century have always held a fascination for the visual media: Jack the Ripper, Jekyll and Hyde, Sherlock Holmes, etc. (The 19th century must be the Golden Age for iconic figures!)
I don’t know if this has been argued before, but I suspect the 19th century episodes of Dr Who were a crucial stimulus to the steampunk mindset. Some of the very best Dr Who stories have been thick with Victoriana atmosphere—“The Talons of Dr Weng Chiang”, for instance. Anyone who grew up with Dr Who (maybe I should re-phrase that—is there anyone who didn’t grow up with Dr Who?) must have come under that influence.
Other influences also worked in subterranean ways, like the TV series Wild Wild West, and Alan Moore’s graphic novel The League of Extraordinary Gentlemen.
The recent movie versions are both great examples of steampunk, though not, alas, great movies. Most people—oh well, me and my writer friends—would say that the movie version of The Golden Compass didn’t live up to the book either.
For movies that a steampunkist can be proud of, I’d name the Japanese anime, Steamboy, and the wonderful French movie, City of Lost Children. I’d add The Prestige too, since it has gadgetry, science and Tesla as well as a 19th century setting. Say, 50% steampunk and 100% success.
City of Ember is retro-future SF, but ends up being fairly close to steampunk.