The point is, the police are (usually) required to have cause to stop motor vehicle drivers, and if they arrest you for DUI after stopping you for no reason, you have grounds to challenge the arrest.
Obviously, "grounds to challenge" is no guarantee that you'll be acquitted or have charges dismissed, and obviously the police can and do manufacture reasons to pull drivers over, but the requirement to have cause creates a disincentive to do that routinely.
Which, my point was, was one reason one might experience stricter detection of DUI's in another country.
