David, the simple fact is that there is a much higher traffic density in Germany, going considerably faster than here and it works. All it would take is a simple stroke of the pen to make people behave differently. That and perhaps a few video cameras to bust the bad guys, since the on ramps are not exactly going anywhere, right ? This is NOT like trying to prosecute a "regular" moving violation, since the violation zone is always in the same place.
The logic is that the guy joining the traffic flow is automatically at a disadvantage compared to the traffic already on the highway. He has to speed up, determine the position of any traffic in his lane, adjust his speed to slide in ahead or behind of any traffic. All the while, people in the right lane are being egotistical maniacs "I'm not letting that #@%&$# in front of me, no way !!!" which complicates things significantly. Giving way to someone merging takes hardly anything at all from someone already on the highway. Maybe he has to let off for 10 seconds to make a space for the other person to slide into. This is NOT a big deal. Done it a million times myself and still do. If NOT letting someone into the right lane had significant consequences (suspension for 3 months or worse) then people would change their behavior.
I'm pretty proud of my German drivers license. It cost several thousand $ to get and included close to 40 hours of instruction, (similar in scope to getting a pilots license). If you fail any part of the syllabus 3 times, the likelihood is very good that you will be permanently banned for life from driving. That is a pretty sobering prospect. Traffic violations here seem to have little in the way of consequences unless you kill or maim someone. The most common one is that it increases the cost of your insurance.