Given that 90% of things that stop you going are easily repaired using basic generic parts (spark plugs, chain links, bits of wire and insulating tape, silver seal etc.) and a large percentage of these simple failures can be fixed with a leatherman then I think it's possible to carry enough stuff to cover virtually every eventuality. Of course, rare failures (on modern bikes) like engine bearings or gearbox failure cannot be predicted nor can electronic failures but if you're really determined it's easy enough to carry replacement parts for the essential electrical/electronic parts (ECU, coil).
I agree that the less there is to fix, the less there is to go wrong. I think the secret to a reliable bike is to replace all the consummable parts before you leave (including the clutch, cables, brake pads and chain/sprockets (if appllicable)) and a major service interval of 2500 to 3000 miles and this should eliminate failures due to poor maintenance - most of the rest is down to luck.
Bikes that need fresh oil every 15 hours aren't really suitable for travelling IMHO