Been looking into this a little more, seems the modern setup is mostly a difference in standards organizations. The full keyboard layout article had quite a bit more information on the differences. US layout is an ANSI standard, while the UK one is an ISO standard. I'm not finding much on the history though. The ANSI layout seems to be derived from the common typewriters, but I'm not finding a similar link for the ISO side.

The Apple differences are also strange. In the US, a PC and Mac keyboard is nearly identical, with the main difference being a swap of where the alt and command/windows keys are.