basil f - I can't point you at the statistics off the top of my head, and I can't be arsed to go looking for the them, but it's a fairly widely known fact that the highest accident rate of all categories occurs in the twin-engine piston category - the FAA has the stats somewhere. Something to do with the "I've got another one which will get me home if one fails" frame of mind. If you've ever flown a light piston twin you will know that most of them need to be VERY well flown to maintain altitude if they are anywhere near gross weight, and most of them won't maintain altitude at a density altitude of anything over about 3000'
You are right though, that if your single Primus goes out with the cloudbase on the deck you're in deep poo!
I reckon they should ban piston twins from public transport IFR too.