Various "experts" tried to fathom this out. The key question was why aircraft in the N Sea were struck relatively often compared to the overall instances of lightning, whereas in other areas with much more lightning (eg Florida, Nigeria) aircraft virtually never got struck.
It seems it was due to the temperature - the voltages needed for lightning are created by charge separation when a mixture of ice and rain separate out in the updraft of a Cb - ice rises because its less dense and rain falls. In order to have this mixture of phases you need to be around zero centigrade - thus this temperature band is where there is the greatest voltage gradient and hence the easiest to trigger the lightning. Of course in the N Sea, operating temperatures are around zero during the winter. The stats show that aircraft on the N Sea are virtually never struck in summer 1/2 of the year, only the winter 1/2.
In the likes of Florida, the zero degree level is way above heli flights, so the only liklihood of getting struck is if you are unlucky enough to be in the way of a cloud to ground strike - very unlikely!
In the N Sea, it seems certain that the aircraft triggers the lighting when it flies through an area of high voltage gradient - the exact mechanism for triggering is not certain but could be either the trail of ionised air resulting from static discharge generated by the rotors, or perhaps an ion trail from the high temperature gases in the exhaust. In either case you are effectively trailing a long conductor behind the aircraft - lightning likes that!
Sorry, the strobe is not an issue as there is no external potential gradient or conductive path. Apart from anything else, if you look at the glass lens of a strobe you will see that there is a wire cage - this is to avoid the emission of radio interference but also eliminates any potential gradient.
The moral is that to avoid getting struck, avoid flying around near zero degrees C - lets say within +- 3 degrees - when lightning is expected. Tricky in winter but it can be done most of the time!
Eurochopper