Is Decopunk separate from Steampunk?

The problem with genres based on aesthetics is knowing where to draw the lines.

Decopunk is considered a subgenre of Dieselpunk set in a more 1920's diesel powered world.  The problem comes in trying to get to the definition of what actually defines a genre.  

I know I am obsessed with literary theory, but these are important questions if we are going to define a genre.  In November, I resolved on a working definition that I am going to use to define steampunk as a literary genre.

A literary subgenre of fantasy featuring a neo-Victorian industrial world where steam and clockwork are the primary sources of power. Technology is retro-futuristic, with a special focus on Repurposing items for uses other than their original intended use. Romanticism and Mysticism form the basis for art, religion, and social values.
No, Seriously, What is Steampunk?

The question is, if steam and clockwork mechanisms power the world, but it has an Art Deco style, does that invalidate a work as steampunk?

Since there are so many pieces of Steampunk Art Deco art on the net that have not met with a cavalcade of criticism and hate, I am inclined to believe that they are aesthetically compatible at least in the way steampunk is drawn.

That is the real problem with trying to pin down this genre.  When something is primarily visual, it is like reading tea leaves to pull out the qualities that would make a story steampunk.

Beyond that, steampunk has been adapted to many visual styles such as Art Nouveau, but yet again, we are looking at the mode in which art is produced rather than the qualities that make it one genre or another. This problem keeps peaking up at me, and makes me question exacting what makes something steampunk.

While steampunk was born out of a neo-Victorian aesthetic, to limit a fantasy subgenre to a terrestrial time period feels overly artificial and pointless.  An art deco building or a flapper girl in a steam powered speakeasy feels as steampunk to me as an adventurer in a bustle, but maybe that is just me.