visual basic dotnet
ComboBox and ListBox both have Items property, and also both are descendants from ListControls
but ListControls have no Items property
do those developers understand object oriented programming correctly?

Could be reasons we do not know.

Maybe there are other list controls that does not implement items.

The real problem with hierarchical components is if you add to much high up that is then not needed.

Thats why there is less hierarchy and more interfaces in C#.

It simplifies reuse without many of the problems with class inheritance.

[edit]
Checked and I think treeview uses a nodes collection instead, probably due to a different item type requirement so you do not try to add an incompatible item to it.