I have the Legend, and it has not got a USB cable, BUT this is not an issue for me, as much as I prefer USB, you are transferring such small bits of data, as a rule, that there is no noticeable delay that I expect with serial.
As far as maps go, I only have the maps that came with it, and haven't bought the TOPO maps yet. Point is, I live in northern Alberta, AKA. middle of nowhere. While a lot of the roads are not on it, once you mark a waypoint for where you are, you can always navigate back to it, and your track will show you the "road" you took to get there. One marked road insists that I am driving through a lake as I go up north, obviously, it's a "remote area" where nobody goes.
Once you understand how to use it, map or no map is less and less of an issue. The map is really a gimmick as far as I am concerned..