My eyes start bleeding when I think too hard about this, but seems in my world inheritance in these cases is being used as a really bad substitute for properties. Which is a lot of 'things' have flat collections of properties not a hierarchy of properties.

I suspect this is why LINQ kinda popular. No one cares if book inherits item. They want to query the random collection of crap someone ordered for 'is a book' or is 'food' so they can properly calculate the sales tax in Minnesota.