Good call Jake. I believe you are correct as we are dealing with Renderers, they only become active when rendered. Interestingly with Flex, this seems to affect the availability of properties as well. For example - try making a control invisible and then access it's properties. Nada... at least in my experience. It's like Flex demartials the object instance when it is not actively being rendered. This might be part of the memory management to keep the flash player running smoothly.
Nice touch, too. I think you're making this easy for a lot of people. With all the articles you're putting together (spoon fed even!) there should be no excuse for any competent developer to not use Flex where it is a good fit. I imagine vast numbers of developers around the world making careers from your teachings. Shouldn't we be calling you Dr. Jake then? ;-)