If I ever meet a German IR holder who says he has never flown in IMC in German Class G, I am going to fall over. If this ban on IFR in Class G was observed strictly, operations from non-IFR airports would grind to a halt, because you would more or less need CAVOK conditions. It's a joke.
The magic word here (in Germany I mean) is _separation_. You are only allowed to fly on instruments alone, where separation can be provided. Either visually or by radar. In IMC this can obviously only be by radar and there is no (guaranteed) radar coverage in class G airspace. We have a very large number of aerodromes in Germany, just look how many pages there are in the "Aiport Directory" section of Jeppesen compared to other countries (which does not even list the countless glider and microlight sites) and at times a high traffic density at low level as well. Flying through this sort of airspace in and out of clouds is not a safe way of flying, therefore I perfectly understand our regulations.
Regarding your "
...who says he has never flown in IMC in German Class G...", well yes, there are always people who stick to the rules and those who don't. Just like you will not find a driver who has never busted a speed limit. But as others have said, those who never flew in IMC at low level have never hit terrain or obstacles...
And regarding the need of CAVOK in order to operate IFR from uncontrolled airfields, this is simply not true. Within class G airspace, all you need 1.5km visibility and be able to stay clear of clouds. For the segment between the lower bounds of class E airspace and the minimum radar vectoring altitude from where the IFR flight starts, reduced minima apply that are identical to class G minima. Which means that from most uncontrolled airfields in Germany you can legally depart with a Z flightplan when you have 1500m visibilty, few in 500ft, scattered in 1500ft and broken in 3000ft. Which is completely different from CAVOK...
Happy landings,
max