I'll be damned if I admit that I noticed it, or really cared about this sort of thing, but Rockstar has made the switch regardless. If it ever bothered you that Grand Theft Auto's GPS counted distances in miles instead of kilometres, Rockstar has kindly granted you the option to switch to the metric system. Amazing.
Apparently this bothered some people. To the point where it must have been a requested option. Personally? It's never bothered me. Probably because I grew up in the UK where distances and speeds are mostly measured in miles. I have a rough idea of those distances and how they convert. Maybe if I grew up in Australia, and had no idea how it all worked, I'd feel a little different.