Who knows? Blame it on the Americans, after all they invented 'British English'. But then the UK does have a mix of metric and statute.
For speed on the device, just set up the datafields appropriately.
Garmin Training Centre will give you both speed and pace so fill your boots.
Garmin Connect will give you pace for running and speed for cycling at the moment.
SportTracks and www.RunSaturday.com will both give you what you want