The Siege of Ironforge, during the 2nd war, lasted months and the Horde never got in. The Horde ended up getting caught in between the Alliance forces that arrived and the rush of dwarves that came flooding out the front gates once it opened suddenly. If anyone wonders why the dwarves are so loyal to Stormwind and the Alliance, they realized they owe their lives to them. 
That would be highly amusing, but also kinda scary. lol
You might be on to something here.
I think my new response to “My, aren’t you a tall one.” is, “I’m only 0.75% taller than you relative to your over compensating ceiling heights”
You could ask the same question about IRL, we build buildings much larger than “needed” for our heights and sizes. It just looks good.
I always thought it was based on Tolkien’s Dwarven architecture.
So I don’t hit my head when I’m up in your base killing your dudes.
How many dwarfs/gnomes does it take to change a light bulb (in Gnomeregan/Iron Forge)?
172, if they stand on each other’s shoulders.
It’s an ego thing. Else the ventilation reasoning makes sense. What with the all that lava, forging, and other gases from the what have you.
If they where lower ceilings then how would the griffins, etc be able to fly/transport players around? There would be no room for them.
So there’s somewhere for all the heat from our decorative channels of lava can go and dissipate.
Do you know how they say a guy with a big sports car is “overcompensating?” It is like that:
We are all so “Squat” that we make our cities with huge ceilings!
Don’t tell anyone, but we’re planning on building the world biggest kegs and having a massive citywide blow-out and BBQ.
For when you have company
Have you seen Eitri?? 
No, don’t even know what that is.
But this is WoW, I demand realism!!!
The fantasy dwarf archetype is the original “Short Guy Who Buys a Big Truck That Everyone Has To Look At” thing. Gnomes are…gnomes.