Don't forget that much of Europe doesn't permit flight under IFR outside CAS in the first place
The essential thing here is that by allowing IFR OCAS the UK acknowledges what is a fait accompli anyway i.e. nobody knows whether you are VMC or IMC when en-route, so no enforcement of any of the VFR rules (clear of cloud, a specified distance from cloud, a specified visibility, in sight of the surface, etc) is possible anyway.
Look at the huge growth of the high-end ultralight and permit categories. A lot of them very well equipped for what is obviously IFR operations. But of course none of these people ever go into a cloud
Not being able to fly IFR OCAS simply means that one cannot request an instrument approach without drawing attention to oneself, in the "not having the JAA IR" department. And one gets stuck at towered airports if the cloudbase is below the VFR departure minima. Other than that, I am sure there is just as much "IFR OCAS" in the rest of Europe as here.
The UK rules go hand in hand with the IMC Rating, which as far as I can tell is close to unique in Europe. Also fairly unique is the anally retentive manner with which Class D is dealt with, being treated as Class B or C, so I think the present situation is just handy for the CAA which really doesn't want to change the airspace management.