I think the case you are making is a little exaggerated. It is not impossible to judge whether something you created is any good or not, without charging for it. The feedback that Joe is getting in the app store is not entirely worthless.
Additionally customers who are not willing to pay aren't necessarily "better" customers. For example in the case of Twitter verus App.net. I'm guessing the people who are willing to pay for App.net are a very selective group of geeky tech nerds. (I'm one of those people.) Listening to those people will lead you to develop a version of Twitter that appeals to them. If you want to develop a version of Twitter that appeals to normal people, charging money will attract the wrong crowd.
Additionally customers who are not willing to pay aren't necessarily "better" customers. For example in the case of Twitter verus App.net. I'm guessing the people who are willing to pay for App.net are a very selective group of geeky tech nerds. (I'm one of those people.) Listening to those people will lead you to develop a version of Twitter that appeals to them. If you want to develop a version of Twitter that appeals to normal people, charging money will attract the wrong crowd.