From what I understand now....having searched other similar discussions is that the warmer the oil the less viscous it is (like water). So with constant short journeys you aren't getting the engine parts fully lubricated because the oil will not flow as easy due to it's thickness (like treacle). These parts are then left with less of a coating when it is started again from cold.
I know that the oil flows back to the bottom of the engine when stopped, but assuming you have let it reach it's optimimum temp eg "a long run", more of a coating will be left on the harder to reach surfaces and will help to lubricate the engine on start up.
If Im not just talking out of my arse
then infrequent driving might also have the same effect or worse but I think the whole thing is minimal tbh and like someone said manufacturers test cars in all conditions and uses so the tolerances are built in to combat this. There will always be good and bad cars in each category of mileage though.
