Engine oil analysis can tell them a lot of things. (If that is what they are doing). For example if they see high quantities of copper in the oil, then it could indicate bearing wear. If you do you own oil changes and aren't using their oil, or the oil level isn't at the right level, they could blame that. They could be looking for an easy out to not change out the motor- if they have to swap an engine, the profit margin from that car is probably null. On the other hand, they could be looking for the answer, in the oil.
It could be something that the oil journals aren't machined large enough, or oil isn't draining fast enough to cool the bearing. If there isn't enough oil, there might not be enough cushioning and the bearing could be getting pounded flat each power stroke it has to deal with, wearing out prematurely.
0w 30 would provide more protection at cold start ups, but some people like gonz probably never have cold starts like we do and he has the same issue. But, maybe its on the other way! Maybe we need a heavier grade oil for more cushioning. Maybe the 30 isnt enough protection. Maybe a 10w 40? But that would cause more wear on cold start... Choices...