It's true, but not exact. Delphi can't interprete code and you should recompile application or make changes of parent class in code. But if you have opened for editing two forms, Form1 and Form2 inherited from Form1, then all changes in Form1 will be immediately reflected in Form2 even before saving of form. When you drop control to Form1 it will appear on Form2, when you move control in Form1 it will be moved in Form2 etc.
Another cool RAD feature of Delphi is ability to work with real data in form and report designers. You can set DataSource properties of control and you will see real data in control before running of form. You can change SQL query and immediately see result, you may change control's size and move columns in a grid accordingly size of real data. It saves a lot of time.

>I was at a demo of Delphi while VFP3 was still in beta, and one of the cool things it did was allow you to edit the class definitions while instances of the class existed. As soon as you saved changes in the designer the objects changed. It was pretty impressive. I have no idea it still works like that or not but it was a cool RAD feature to have available during development.
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>>Well it would get worse though - if you modify one of the base classes while you're editing one of the descendent classes you'd essentially be working on an invalid copy missing properties and methods possibly...