OK, we've been talking theoretically about books and kits. Now, here is a real world example.
As you can see from this list, the parts used in my Endangered Species robots are all very common parts--it's all a problem of quantities. In fact, I first designed all of these robots for the 2.0 kit, but modified them so teachers and FLL leaders could use them.
Does a parts list like this make no one happy...everyone happy...?