BMW has many more expensive models than the 3 series models. 5, 7, 8s are all much more expensive. Perhaps that is how the average 10 year cost is greater than the 328s?
Sure, but shouldn't the 5/6/7 series then appear as the highest-cost models rather than the 328i?
The article doesn't really explain things very well. Why did they only pick those 20 models to compare? I think they are all in the same price range? This is probably appealing to "mainstream" models, rather than enthusiast or luxury models.