Higher voltage = smaller wire diameter.

[Richard Crowley]

Here in the UK, a transformer normally powers a whole block of houses or more. Most wiring in the street is 400V/230VAC.

Yes, of course, how provincial of me. Not only is end-user distribution done at higher voltage (230V/440V)  vs 120 here in the colonies, but the loads/users tend to be much closer together. 
And the UK is much more space-efficient. You guys manage to fit an entire country into the space we waste on just my state (Oregon).

[IanB]

That depends on where you live. Here in the UK, a transformer normally powers a whole block of houses or more. Most wiring in the street is 400V/230VAC.

That is true, the wiring from the local substation to houses is three phase 415/240 V, with phases alternating between houses to balance the load. Even so, there is very likely an 11 kV feeder running under many streets to supply the substations.

When these subsurface 11 kV feeders get old and fail they create a very exciting bang under the pavement (sidewalk) that can cause passing pedestrians to jump out of their skins 

[Macbeth]

I am here in Oregon, the northern end of the 3.1 MW Pacific DC Intertie.

I think you mean 3.1 GW (3,100 MW). 3.1 MW is barely enough to electrocute a flea... 

3.1GW? Holy shit. That's enough jiggerwatts to power at least 2x DeLorean time machines (2.42GW would be enough).

But, TIL there is DC transmission of such power! I thought Tesla proved Edison wrong all this time.

[coppice]

Here in the UK, a transformer normally powers a whole block of houses or more. Most wiring in the street is 400V/230VAC.

Yes, of course, how provincial of me. Not only is end-user distribution done at higher voltage (230V/440V)  vs 120 here in the colonies, but the loads/users tend to be much closer together. 
And the UK is much more space-efficient. You guys manage to fit an entire country into the space we waste on just my state (Oregon).

The US has an average of 4 homes per transformer across the whole country. In many areas its 1:1. Only the most rural of locations in countries using 220V/230V are like that. Even affluent suburban areas, where the houses are well spread out, have a couple of streets per transformer.

America pays for its low mains voltage in the very slow production of tea and toast. 

[Macbeth]

America pays for its low mains voltage in the very slow production of tea and toast. 

Yes, I have often considered emigrating to the USA, but for the insane police state, religious nuttery, and absurd healthcare. It was the fact I can't make a decent cup of tea or toast my crumpets efficiently that was the final nail in the coffin.