One of the many complaints I've heard about a variety of Steampunk works is that certain aspects that are integral to Steampunk, i.e. the technology of your typical Steampunk society, appear to be mere "window dressing" so you can call the story a Steampunk novel. Steam tanks just to have steam tanks; dirigibles because those are always in Steampunk stories; and even fancy gadgets that have no real purpose other than to look ... well, fancy.
Now, these "window dressing" stories are the kinds of novels that can happen in any time frame with any level of technology. They're in a sense timeless, but they're also not very grounded in their particular world. This is distinct from translating a story into another, related subgenre of the same overarching genre -- a la taking an Urban Fantasy such as Storm Front by Jim Butcher and switching a few aspects to make it a faux-Medieval Fantasy.
Think rather of a Romance or a Detective novel where the characters use advanced mechanical technology that has no reason to not be powered by electricity instead. Like the gear-based zoom binoculars that can easily be replaced by digital binoculars without impacting the story. Or the adventure story where the airship voyage can easily be replaced by a plane ride or an ocean liner. Essentially, the "window dressing" Steampunk tale doesn't integrate the technology into the world of the story in a real way.
A good example of where the technology is necessary is in Dreadnought by Cherie Priest. Without the airship, Vinita Lynch wouldn't have been able to evade the battlegrounds that were evaded and the story would have needed to include scenes of her getting around the fighting instead of allowing her to fly over it. A counter-example, where the technology isn't quite so integrated into the story, would be a tale where the POV character merely sees an airship floating overhead and never actually goes near one.
You could argue that Steampunk as "window dressing" violates the Chekhov's Gun law of fiction, in point of fact. Chekhov's Gun, for those who don't know, comes from a statement made by Russian playwright, short-story writer, and physician Anton Chekhov in his memoirs (published 1911). Chekhov's rule states that "If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off. If it's not going to be fired, it shouldn't be hanging there." (from TVtropes.org)
The rule applies to pretty much everything in your story, particularly as it relates to description of the scene around your characters. Chekhov was of the belief that, if a detail didn't serve a purpose then it shouldn't be mentioned anywhere within the text. If the author spends a full paragraph describing something in loving detail and then never mentions it again, then that's a violation of Chekhov's Gun. So it is with Steampunk as "window dressing" in stories. If the elements don't serve an integral part to the story, then they don't need to be there.
Steampunk as "window dressing" could almost be called a bandwagon move. As Steampunk is on the rise in popularity, there are certain people who are of the belief that if you throw a few cogs and goggles into a story then it's automatically Steampunk. This violates both the concept of Chekhov's Gun and dilutes the notion of Steampunk as a valid subgenre when its aesthetic is co-opted as "window dressing." It also gives those writers who consider the world of their story before including Steampunk elements a very bad name. Now, I'm not saying you need to discuss the socioeconomic impact of Steampunk innovations on the populace and that's the only valid use of the aesthetic, but rather to merely consider whether something is really necessary to move your story forward.
NOTE: I'll be discussing this very topic, co-hosted by Steampunk Writers & Artists Guild Founder Lia Keyes, tonight on Twitter at 9 p.m. U.S. Eastern Time/6 p.m. U.S. Pacific Time. Follow the hashtag #steampunkchat if you want to participate.