Why do only US makers focus on time coherency?

Tannoy.

you mention Thiel twice!?

* JM Lab is time coherent but not phase coherent.
* German make "Manger" is a single driver speaker & by its very nature is time & phase coherent.
* Taiwanese make "Usher" appears to be time-coherent esp. from the looks of their floor standing speakers' sloped baffle. Looks could be deceiving tho' - I have never heard this brand.

It's because the Brits are on Greenich mean time, and we're not.
From B&W's website: Tweeter on top reduces time smearing by allowing driver time alignment and reducing diffraction at the cabinet edges.

That's a very good question. The british speakers seem to be more interested in smooth frequency response, than time and phase. To date I haven't heard a british speaker that images particularly well (and don't say ls3/5 because they don't image at all !)

As a brit myself I find my compatriots' fascination with this thing called PRAT to be a bit odd. Why are we so quick to throw out spatial information to try to make the music bouncy ? Perhaps because fewer brits have the space in their houses to allow for speaker positioning that would allow imaging ?