if you do not think it is steampunk than what genre or mixture of genres would you describe it as?
I'd describe it as fantasy, but there are a few elements that might appeal to the same people who like steampunk, or turn off people who don't. It's primarily a fantasy world built around the D&D ruleset, with a few tweaks to set it apart from other generic-fantasy settings like Greyhawk and Forgotten Realms.
"Steampunk" generally refers to a Victorian-style setting where industrial age technology is combined with magic. It usually includes strong themes of magic/nature vs. technology. Guns are a common thing to include, and 19th-century clothing is common. Eberron includes none of the above.
Eberron
is a world where applied magic has grown in place of applied science. There won't be magic telephones or magic cars (unless you decide to homebrew them), but the spells in the Player's Handbook have been applied in logical ways. Major cities will have
continual flame streetlights. A new NPC class, the magewright, has access to cantrips and minor spells that improve the speed and quality of basic crafting. The unusually magical city of Sharn has magically-augmented architecture and a network of levitating stone platforms. This is all pretty "high magic" stuff, but it's not ubiquitous, and it only goes up to a certain level. War is still fought with swords and bows, teleportation networks do not exist, and the highest level (friendly) NPC is a 16th-level cleric who can't leave her god's temple.
Eberron does feature some elements that remind people of steampunk. One is a race of living constructs called
warforged. They're made of wood and metal, but they're animated through magic rather than gears and electricity. To some people they're still too much like "robots," but they're presented as golems with souls. There are also
airships, but they aren't zeppelins or steam-powered iron. They are medieval-looking ships powered by bound elementals. Finally, there's the
Lightning Rail, which is the one example of a magically-enhanced device that's decidedly anachronistic-looking. Again, though, it's a bunch of stone and iron that levitates along a path, not an example of an engine that transforms magic into propulsion, or something. The Lightning Rail system is also a unique, wondrous thing that doesn't represent the overall look of the world.
Personally, I see the above stuff as flavor. It's good as long as it's integrated well, and the preview materials suggest to me that it will be. If it intruded on mechanics, if anyone could build mana-powered engines or characters carried guns, that would cross the line into "not D&D." Check out the Eberron Journal's
gallery of concept art. None of that stuff says "not D&D" to me.