It's not clear to me where the word "helloworld" refers to in these examples. Can you please clarify when 'helloworld' refers to the component,controller,model,table,view or form? While following this, I've changed the name of my component, and when running this I get a 'call to member function getTable() on non-object'. It seems that I used the wrong name somewhere, but I have no idea where.
We're also introducing JForms and JFields. These are powerful and important, and warrant some richer explanation.
There is a change in /admin/views/helloworlds/tmpl/default_body.php that isnt mentioned on this page but is present in the archive file.
Note that the model loaded in the getModel function by the HelloWorlds controller (admin/controllers/helloworlds.php) is NOT the HelloWorlds model; it is instead the HelloWorld model. The HelloWorlds model (HelloWorldModelHelloWorlds) extends JModelList, which has no delete function. The HelloWorld model (HelloWorldModelHelloWorld) extends JModelAdmin, which has the delete function needed to delete items.