My dog frequently does this-it is like she is pondering my words. I have seen quite a few dogs doing this…anybody know why?
Ar? 
It’s because you’re talking to them in a language they don’t understand as though they do understand it.
“What’s this damn human doing talking to me again? He knows I can’t understand him. Idiot.”
Something like that. 
It’s funny when they do it and I’ve always thought it was because of the same reasons humans do it too. This article seems to agree.
Baroo?
I can think of two reasons:
First, it positions her head so she can better hear what you’re saying. Your voice is an important sound to her, so she wants to listen closely. You’ll also see dogs doing something similar when there’s a distant sound of interest.
Second, it’s a social cue to let you know that she’s listening to you. Dogs, like humans, are social animals, and so have evolved ways to better communicate with each other.
If a droopy-eared dog tilts his head, the ear will dangle further from the head letting more sound in. It’s kind of the equivalent to a human removing one earbud from his iPod while talking to you.
Marcie’s dog never does the head cocking thing. He does, when I’m close enough, do the leg cocking thing, though.
Your dog comes from a long line of service dogs. He’s lip reading to stay in practice.
That’s when he’s looking at your arse.
This is a fallacy, the dogs keep their head fixed and YOU tip your head when you talk to them but you don’t realize this so it appears THE DOG cocked his head.
I always assumed it was my dogs way of communicating to me that she knows I’m an idiot.
I call it her WTF? face.
Dogs think human words work on gravity,most of the time we are talking down to them. They tip their head so that the words go in one ear and out the other.
Arf!
It’s weird that they think in English, but can’t understand when I speak it.
I was translating. 
I wouldn’t be surprised if the answer is something along the lines of:
- Traditionally it happened when a dog would try to orient one ear on you.
- However, this also happens to look cute, making dogs who did this more liked by humans and hence more likely to be bred.
Goren impressions.
Imitating David Caruso
But dogs are naturally good actors.